.. XXX: reference/datamodel and this have quite a few overlaps!

.. _bltin-types:

Built-in Types

The following sections describe the standard types that are built into the interpreter.

.. index:: pair: built-in; types

The principal built-in types are numerics, sequences, mappings, classes, instances and exceptions.

Some collection classes are mutable. The methods that add, subtract, or rearrange their members in place, and don't return a specific item, never return the collection instance itself but None.

Some operations are supported by several object types; in particular, practically all objects can be compared for equality, tested for truth value, and converted to a string (with the :func:repr function or the slightly different :func:str function). The latter function is implicitly used when an object is written by the :func:print function.

.. _truth:

Truth Value Testing

.. index:: pair: statement; if pair: statement; while pair: truth; value pair: Boolean; operations single: false

Any object can be tested for truth value, for use in an :keyword:if or :keyword:while condition or as operand of the Boolean operations below.

.. index:: single: true

By default, an object is considered true unless its class defines either a :meth:~object.__bool__ method that returns False or a :meth:~object.__len__ method that returns zero, when called with the object. [1]_ If one of the methods raises an exception when called, the exception is propagated and the object does not have a truth value (for example, :data:NotImplemented). Here are most of the built-in objects considered false:

.. index:: single: None (Built-in object) single: False (Built-in object)

constants defined to be false: None and False
zero of any numeric type: 0, 0.0, 0j, Decimal(0), Fraction(0, 1)
empty sequences and collections: '', (), [], {}, set(), range(0)

.. index:: pair: operator; or pair: operator; and single: False single: True

Operations and built-in functions that have a Boolean result always return 0 or False for false and 1 or True for true, unless otherwise stated. (Important exception: the Boolean operations or and and always return one of their operands.)

.. _boolean:

Boolean Operations --- :keyword:`!and`, :keyword:`!or`, :keyword:`!not`

.. index:: pair: Boolean; operations

These are the Boolean operations, ordered by ascending priority:

+-------------+---------------------------------+-------+ | Operation | Result | Notes | +=============+=================================+=======+ | x or y | if x is true, then x, else | (1) | | | y | | +-------------+---------------------------------+-------+ | x and y | if x is false, then x, else | (2) | | | y | | +-------------+---------------------------------+-------+ | not x | if x is false, then True, | (3) | | | else False | | +-------------+---------------------------------+-------+

.. index:: pair: operator; and pair: operator; or pair: operator; not

Notes:

(1) This is a short-circuit operator, so it only evaluates the second argument if the first one is false.

(2) This is a short-circuit operator, so it only evaluates the second argument if the first one is true.

(3) not has a lower priority than non-Boolean operators, so not a == b is interpreted as not (a == b), and a == not b is a syntax error.

.. _stdcomparisons:

Comparisons

.. index:: pair: chaining; comparisons pair: operator; comparison pair: operator; == pair: operator; < (less) pair: operator; <= pair: operator; > (greater) pair: operator; >= pair: operator; != pair: operator; is pair: operator; is not

There are eight comparison operations in Python. They all have the same priority (which is higher than that of the Boolean operations). Comparisons can be chained arbitrarily; for example, x < y <= z is equivalent to x < y and y <= z, except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false).

This table summarizes the comparison operations:

+------------+-------------------------+ | Operation | Meaning | +============+=========================+ | < | strictly less than | +------------+-------------------------+ | <= | less than or equal | +------------+-------------------------+ | > | strictly greater than | +------------+-------------------------+ | >= | greater than or equal | +------------+-------------------------+ | == | equal | +------------+-------------------------+ | != | not equal | +------------+-------------------------+ | is | object identity | +------------+-------------------------+ | is not | negated object identity | +------------+-------------------------+

.. index:: pair: object; numeric pair: objects; comparing

Unless stated otherwise, objects of different types never compare equal. The == operator is always defined but for some object types (for example, class objects) is equivalent to :keyword:is. The <, <=, > and >= operators are only defined where they make sense; for example, they raise a :exc:TypeError exception when one of the arguments is a complex number.

.. index:: single: eq() (instance method) single: ne() (instance method) single: lt() (instance method) single: le() (instance method) single: gt() (instance method) single: ge() (instance method)

Non-identical instances of a class normally compare as non-equal unless the class defines the :meth:~object.__eq__ method.

Instances of a class cannot be ordered with respect to other instances of the same class, or other types of object, unless the class defines enough of the methods :meth:~object.__lt__, :meth:~object.__le__, :meth:~object.__gt__, and :meth:~object.__ge__ (in general, :meth:~object.__lt__ and :meth:~object.__eq__ are sufficient, if you want the conventional meanings of the comparison operators).

The behavior of the :keyword:is and :keyword:is not operators cannot be customized; also they can be applied to any two objects and never raise an exception.

.. index:: pair: operator; in pair: operator; not in

Two more operations with the same syntactic priority, :keyword:in and :keyword:not in, are supported by types that are :term:iterable or implement the :meth:~object.__contains__ method.

.. _typesnumeric:

Numeric Types --- :class:`int`, :class:`float`, :class:`complex`

.. index:: pair: object; numeric pair: object; Boolean pair: object; integer pair: object; floating-point pair: object; complex number pair: C; language

There are three distinct numeric types: :dfn:integers, :dfn:floating-point numbers, and :dfn:complex numbers. In addition, Booleans are a subtype of integers. Integers have unlimited precision. Floating-point numbers are usually implemented using :c:expr:double in C; information about the precision and internal representation of floating-point numbers for the machine on which your program is running is available in :data:sys.float_info. Complex numbers have a real and imaginary part, which are each a floating-point number. To extract these parts from a complex number z, use z.real and z.imag. (The standard library includes the additional numeric types :mod:fractions.Fraction, for rationals, and :mod:decimal.Decimal, for floating-point numbers with user-definable precision.)

.. index:: pair: numeric; literals pair: integer; literals pair: floating-point; literals pair: complex number; literals pair: hexadecimal; literals pair: octal; literals pair: binary; literals

Numbers are created by numeric literals or as the result of built-in functions and operators. Unadorned integer literals (including hex, octal and binary numbers) yield integers. Numeric literals containing a decimal point or an exponent sign yield floating-point numbers. Appending 'j' or 'J' to a numeric literal yields an imaginary number (a complex number with a zero real part) which you can add to an integer or float to get a complex number with real and imaginary parts.

The constructors :func:int, :func:float, and :func:complex can be used to produce numbers of a specific type.

.. index:: single: arithmetic pair: built-in function; int pair: built-in function; float pair: built-in function; complex single: operator; + (plus) single: + (plus); unary operator single: + (plus); binary operator single: operator; - (minus) single: - (minus); unary operator single: - (minus); binary operator pair: operator; * (asterisk) pair: operator; / (slash) pair: operator; // pair: operator; % (percent) pair: operator; **

.. _stdtypes-mixed-arithmetic:

Python fully supports mixed arithmetic: when a binary arithmetic operator has operands of different built-in numeric types, the operand with the "narrower" type is widened to that of the other:

If both arguments are complex numbers, no conversion is performed;
if either argument is a complex or a floating-point number, the other is converted to a floating-point number;
otherwise, both must be integers and no conversion is necessary.

Arithmetic with complex and real operands is defined by the usual mathematical formula, for example::

x + complex(u, v) = complex(x + u, v)
x * complex(u, v) = complex(x * u, x * v)

A comparison between numbers of different types behaves as though the exact values of those numbers were being compared. [2]_

All numeric types (except complex) support the following operations (for priorities of the operations, see :ref:operator-summary):

+---------------------+---------------------------------+---------+--------------------+ | Operation | Result | Notes | Full documentation | +=====================+=================================+=========+====================+ | x + y | sum of x and y | | | +---------------------+---------------------------------+---------+--------------------+ | x - y | difference of x and y | | | +---------------------+---------------------------------+---------+--------------------+ | x * y | product of x and y | | | +---------------------+---------------------------------+---------+--------------------+ | x / y | quotient of x and y | | | +---------------------+---------------------------------+---------+--------------------+ | x // y | floored quotient of x and | (1)(2)| | | | y | | | +---------------------+---------------------------------+---------+--------------------+ | x % y | remainder of x / y | (2) | | +---------------------+---------------------------------+---------+--------------------+ | -x | x negated | | | +---------------------+---------------------------------+---------+--------------------+ | +x | x unchanged | | | +---------------------+---------------------------------+---------+--------------------+ | abs(x) | absolute value or magnitude of | | :func:abs | | | x | | | +---------------------+---------------------------------+---------+--------------------+ | int(x) | x converted to integer | (3)(6)| :func:int | +---------------------+---------------------------------+---------+--------------------+ | float(x) | x converted to floating point | (4)(6)| :func:float | +---------------------+---------------------------------+---------+--------------------+ | complex(re, im) | a complex number with real part | (6) | :func:complex | | | re, imaginary part im. | | | | | im defaults to zero. | | | +---------------------+---------------------------------+---------+--------------------+ | c.conjugate() | conjugate of the complex number | | | | | c | | | +---------------------+---------------------------------+---------+--------------------+ | divmod(x, y) | the pair (x // y, x % y) | (2) | :func:divmod | +---------------------+---------------------------------+---------+--------------------+ | pow(x, y) | x to the power y | (5) | :func:pow | +---------------------+---------------------------------+---------+--------------------+ | x ** y | x to the power y | (5) | | +---------------------+---------------------------------+---------+--------------------+

.. index:: triple: operations on; numeric; types single: conjugate() (complex number method)

Notes:

(1) Also referred to as integer division. For operands of type :class:int, the result has type :class:int. For operands of type :class:float, the result has type :class:float. In general, the result is a whole integer, though the result's type is not necessarily :class:int. The result is always rounded towards minus infinity: 1//2 is 0, (-1)//2 is -1, 1//(-2) is -1, and (-1)//(-2) is 0.

(2) Not for complex numbers. Instead convert to floats using :func:abs if appropriate.

(3) .. index:: pair: module; math single: floor() (in module math) single: ceil() (in module math) single: trunc() (in module math) pair: numeric; conversions

Conversion from :class:float to :class:int truncates, discarding the fractional part. See functions :func:math.floor and :func:math.ceil for alternative conversions.

(4) float also accepts the strings "nan" and "inf" with an optional prefix "+" or "-" for Not a Number (NaN) and positive or negative infinity.

(5) Python defines pow(0, 0) and 0 ** 0 to be 1, as is common for programming languages.

(6) The numeric literals accepted include the digits 0 to 9 or any Unicode equivalent (code points with the Nd property).

See the Unicode Standard <https://unicode.org/Public/UNIDATA/extracted/DerivedNumericType.txt>_ for a complete list of code points with the Nd property.

All :class:numbers.Real types (:class:int and :class:float) also include the following operations:

For additional numeric operations see the :mod:math and :mod:cmath modules.

.. XXXJH exceptions: overflow (when? what operations?) zerodivision

.. _bitstring-ops:

Bitwise Operations on Integer Types

.. index:: triple: operations on; integer; types pair: bitwise; operations pair: shifting; operations pair: masking; operations pair: operator; | (vertical bar) pair: operator; ^ (caret) pair: operator; & (ampersand) pair: operator; << pair: operator; >> pair: operator; ~ (tilde)

Bitwise operations only make sense for integers. The result of bitwise operations is calculated as though carried out in two's complement with an infinite number of sign bits.

The priorities of the binary bitwise operations are all lower than the numeric operations and higher than the comparisons; the unary operation ~ has the same priority as the other unary numeric operations (+ and -).

This table lists the bitwise operations sorted in ascending priority:

+------------+--------------------------------+----------+ | Operation | Result | Notes | +============+================================+==========+ | x | y | bitwise :dfn:or of x and | (4) | | | y | | +------------+--------------------------------+----------+ | x ^ y | bitwise :dfn:exclusive or of | (4) | | | x and y | | +------------+--------------------------------+----------+ | x & y | bitwise :dfn:and of x and | (4) | | | y | | +------------+--------------------------------+----------+ | x << n | x shifted left by n bits | (1)(2) | +------------+--------------------------------+----------+ | x >> n | x shifted right by n bits | (1)(3) | +------------+--------------------------------+----------+ | ~x | the bits of x inverted | | +------------+--------------------------------+----------+

Notes:

(1) Negative shift counts are illegal and cause a :exc:ValueError to be raised.

(2) A left shift by n bits is equivalent to multiplication by pow(2, n).

(3) A right shift by n bits is equivalent to floor division by pow(2, n).

(4) Performing these calculations with at least one extra sign extension bit in a finite two's complement representation (a working bit-width of 1 + max(x.bit_length(), y.bit_length()) or more) is sufficient to get the same result as if there were an infinite number of sign bits.

Additional Methods on Integer Types

The int type implements the :class:numbers.Integral :term:abstract base class. In addition, it provides a few more methods:

.. method:: int.bit_length()

Return the number of bits necessary to represent an integer in binary,
excluding the sign and leading zeros::

    >>> n = -37
    >>> bin(n)
    '-0b100101'
    >>> n.bit_length()
    6

More precisely, if ``x`` is nonzero, then ``x.bit_length()`` is the
unique positive integer ``k`` such that ``2**(k-1) <= abs(x) < 2**k``.
Equivalently, when ``abs(x)`` is small enough to have a correctly
rounded logarithm, then ``k = 1 + int(log(abs(x), 2))``.
If ``x`` is zero, then ``x.bit_length()`` returns ``0``.

Equivalent to::

    def bit_length(self):
        s = bin(self)       # binary representation:  bin(-37) --> '-0b100101'
        s = s.lstrip('-0b') # remove leading zeros and minus sign
        return len(s)       # len('100101') --> 6

.. versionadded:: 3.1

.. method:: int.bit_count()

Return the number of ones in the binary representation of the absolute
value of the integer. This is also known as the population count.
Example::

    >>> n = 19
    >>> bin(n)
    '0b10011'
    >>> n.bit_count()
    3
    >>> (-n).bit_count()
    3

Equivalent to::

    def bit_count(self):
        return bin(self).count("1")

.. versionadded:: 3.10

.. method:: int.to_bytes(length=1, byteorder='big', *, signed=False)

Return an array of bytes representing an integer.

    >>> (1024).to_bytes(2, byteorder='big')
    b'\x04\x00'
    >>> (1024).to_bytes(10, byteorder='big')
    b'\x00\x00\x00\x00\x00\x00\x00\x00\x04\x00'
    >>> (-1024).to_bytes(10, byteorder='big', signed=True)
    b'\xff\xff\xff\xff\xff\xff\xff\xff\xfc\x00'
    >>> x = 1000
    >>> x.to_bytes((x.bit_length() + 7) // 8, byteorder='little')
    b'\xe8\x03'

The integer is represented using *length* bytes, and defaults to 1.  An
:exc:`OverflowError` is raised if the integer is not representable with
the given number of bytes.

The *byteorder* argument determines the byte order used to represent the
integer, and defaults to ``"big"``.  If *byteorder* is
``"big"``, the most significant byte is at the beginning of the byte
array.  If *byteorder* is ``"little"``, the most significant byte is at
the end of the byte array.

The *signed* argument determines whether two's complement is used to
represent the integer.  If *signed* is ``False`` and a negative integer is
given, an :exc:`OverflowError` is raised. The default value for *signed*
is ``False``.

The default values can be used to conveniently turn an integer into a
single byte object::

    >>> (65).to_bytes()
    b'A'

However, when using the default arguments, don't try
to convert a value greater than 255 or you'll get an :exc:`OverflowError`.

Equivalent to::

    def to_bytes(n, length=1, byteorder='big', signed=False):
        if byteorder == 'little':
            order = range(length)
        elif byteorder == 'big':
            order = reversed(range(length))
        else:
            raise ValueError("byteorder must be either 'little' or 'big'")

        return bytes((n >> i*8) & 0xff for i in order)

.. versionadded:: 3.2
.. versionchanged:: 3.11
   Added default argument values for ``length`` and ``byteorder``.

.. classmethod:: int.from_bytes(bytes, byteorder='big', *, signed=False)

Return the integer represented by the given array of bytes.

    >>> int.from_bytes(b'\x00\x10', byteorder='big')
    16
    >>> int.from_bytes(b'\x00\x10', byteorder='little')
    4096
    >>> int.from_bytes(b'\xfc\x00', byteorder='big', signed=True)
    -1024
    >>> int.from_bytes(b'\xfc\x00', byteorder='big', signed=False)
    64512
    >>> int.from_bytes([255, 0, 0], byteorder='big')
    16711680

The argument *bytes* must either be a :term:`bytes-like object` or an
iterable producing bytes.

The *byteorder* argument determines the byte order used to represent the
integer, and defaults to ``"big"``.  If *byteorder* is
``"big"``, the most significant byte is at the beginning of the byte
array.  If *byteorder* is ``"little"``, the most significant byte is at
the end of the byte array.  To request the native byte order of the host
system, use :data:`sys.byteorder` as the byte order value.

The *signed* argument indicates whether two's complement is used to
represent the integer.

Equivalent to::

    def from_bytes(bytes, byteorder='big', signed=False):
        if byteorder == 'little':
            little_ordered = list(bytes)
        elif byteorder == 'big':
            little_ordered = list(reversed(bytes))
        else:
            raise ValueError("byteorder must be either 'little' or 'big'")

        n = sum(b << i*8 for i, b in enumerate(little_ordered))
        if signed and little_ordered and (little_ordered[-1] & 0x80):
            n -= 1 << 8*len(little_ordered)

        return n

.. versionadded:: 3.2
.. versionchanged:: 3.11
   Added default argument value for ``byteorder``.

.. method:: int.as_integer_ratio()

Return a pair of integers whose ratio is equal to the original integer and has a positive denominator. The integer ratio of integers (whole numbers) is always the integer as the numerator and 1 as the denominator.

.. versionadded:: 3.8

.. method:: int.is_integer()

Returns True. Exists for duck type compatibility with :meth:float.is_integer.

.. versionadded:: 3.12

Additional Methods on Float

The float type implements the :class:numbers.Real :term:abstract base class. float also has the following additional methods.

.. classmethod:: float.from_number(x)

Class method to return a floating-point number constructed from a number x.

If the argument is an integer or a floating-point number, a floating-point number with the same value (within Python's floating-point precision) is returned. If the argument is outside the range of a Python float, an :exc:OverflowError will be raised.

For a general Python object x, float.from_number(x) delegates to x.__float__(). If :meth:~object.__float__ is not defined then it falls back to :meth:~object.__index__.

.. versionadded:: 3.14

.. method:: float.as_integer_ratio()

Return a pair of integers whose ratio is exactly equal to the original float. The ratio is in lowest terms and has a positive denominator. Raises :exc:OverflowError on infinities and a :exc:ValueError on NaNs.

.. method:: float.is_integer()

Return True if the float instance is finite with integral value, and False otherwise::

  >>> (-2.0).is_integer()
  True
  >>> (3.2).is_integer()
  False

Two methods support conversion to and from hexadecimal strings. Since Python's floats are stored internally as binary numbers, converting a float to or from a decimal string usually involves a small rounding error. In contrast, hexadecimal strings allow exact representation and specification of floating-point numbers. This can be useful when debugging, and in numerical work.

.. method:: float.hex()

Return a representation of a floating-point number as a hexadecimal string. For finite floating-point numbers, this representation will always include a leading 0x and a trailing p and exponent.

.. classmethod:: float.fromhex(s)

Class method to return the float represented by a hexadecimal string s. The string s may have leading and trailing whitespace.

Note that :meth:float.hex is an instance method, while :meth:float.fromhex is a class method.

A hexadecimal string takes the form::

[sign] ['0x'] integer ['.' fraction] ['p' exponent]

where the optional sign may by either + or -, integer and fraction are strings of hexadecimal digits, and exponent is a decimal integer with an optional leading sign. Case is not significant, and there must be at least one hexadecimal digit in either the integer or the fraction. This syntax is similar to the syntax specified in section 6.4.4.2 of the C99 standard, and also to the syntax used in Java 1.5 onwards. In particular, the output of :meth:float.hex is usable as a hexadecimal floating-point literal in C or Java code, and hexadecimal strings produced by C's %a format character or Java's Double.toHexString are accepted by :meth:float.fromhex.

Note that the exponent is written in decimal rather than hexadecimal, and that it gives the power of 2 by which to multiply the coefficient. For example, the hexadecimal string 0x3.a7p10 represents the floating-point number (3 + 10./16 + 7./16**2) * 2.0**10, or 3740.0::

float.fromhex('0x3.a7p10') 3740.0

Applying the reverse conversion to 3740.0 gives a different hexadecimal string representing the same number::

float.hex(3740.0) '0x1.d380000000000p+11'

Additional Methods on Complex

The :class:!complex type implements the :class:numbers.Complex :term:abstract base class. :class:!complex also has the following additional methods.

.. classmethod:: complex.from_number(x)

Class method to convert a number to a complex number.

For a general Python object x, complex.from_number(x) delegates to x.__complex__(). If :meth:~object.__complex__ is not defined then it falls back to :meth:~object.__float__. If :meth:!__float__ is not defined then it falls back to :meth:~object.__index__.

.. versionadded:: 3.14

.. _numeric-hash:

Hashing of numeric types

For numbers x and y, possibly of different types, it's a requirement that hash(x) == hash(y) whenever x == y (see the :meth:~object.__hash__ method documentation for more details). For ease of implementation and efficiency across a variety of numeric types (including :class:int, :class:float, :class:decimal.Decimal and :class:fractions.Fraction) Python's hash for numeric types is based on a single mathematical function that's defined for any rational number, and hence applies to all instances of :class:int and :class:fractions.Fraction, and all finite instances of :class:float and :class:decimal.Decimal. Essentially, this function is given by reduction modulo P for a fixed prime P. The value of P is made available to Python as the :attr:~sys.hash_info.modulus attribute of :data:sys.hash_info.

.. impl-detail::

Currently, the prime used is P = 2**31 - 1 on machines with 32-bit C longs and P = 2**61 - 1 on machines with 64-bit C longs.

Here are the rules in detail:

If x = m / n is a nonnegative rational number and n is not divisible by P, define hash(x) as m * invmod(n, P) % P, where invmod(n, P) gives the inverse of n modulo P.
If x = m / n is a nonnegative rational number and n is divisible by P (but m is not) then n has no inverse modulo P and the rule above doesn't apply; in this case define hash(x) to be the constant value sys.hash_info.inf.
If x = m / n is a negative rational number define hash(x) as -hash(-x). If the resulting hash is -1, replace it with -2.
The particular values sys.hash_info.inf and -sys.hash_info.inf are used as hash values for positive infinity or negative infinity (respectively).
For a :class:complex number z, the hash values of the real and imaginary parts are combined by computing hash(z.real) + sys.hash_info.imag * hash(z.imag), reduced modulo 2**sys.hash_info.width so that it lies in range(-2**(sys.hash_info.width - 1), 2**(sys.hash_info.width - 1)). Again, if the result is -1, it's replaced with -2.

To clarify the above rules, here's some example Python code, equivalent to the built-in hash, for computing the hash of a rational number, :class:float, or :class:complex::

import sys, math

def hash_fraction(m, n): """Compute the hash of a rational number m / n.

   Assumes m and n are integers, with n positive.
   Equivalent to hash(fractions.Fraction(m, n)).

   """
   P = sys.hash_info.modulus
   # Remove common factors of P.  (Unnecessary if m and n already coprime.)
   while m % P == n % P == 0:
       m, n = m // P, n // P

   if n % P == 0:
       hash_value = sys.hash_info.inf
   else:
       # Fermat's Little Theorem: pow(n, P-1, P) is 1, so
       # pow(n, P-2, P) gives the inverse of n modulo P.
       hash_value = (abs(m) % P) * pow(n, P - 2, P) % P
   if m < 0:
       hash_value = -hash_value
   if hash_value == -1:
       hash_value = -2
   return hash_value

def hash_float(x): """Compute the hash of a float x."""

   if math.isnan(x):
       return object.__hash__(x)
   elif math.isinf(x):
       return sys.hash_info.inf if x > 0 else -sys.hash_info.inf
   else:
       return hash_fraction(*x.as_integer_ratio())

def hash_complex(z): """Compute the hash of a complex number z."""

   hash_value = hash_float(z.real) + sys.hash_info.imag * hash_float(z.imag)
   # do a signed reduction modulo 2**sys.hash_info.width
   M = 2**(sys.hash_info.width - 1)
   hash_value = (hash_value & (M - 1)) - (hash_value & M)
   if hash_value == -1:
       hash_value = -2
   return hash_value

.. _bltin-boolean-values: .. _typebool:

Boolean Type - :class:`bool`

Booleans represent truth values. The :class:bool type has exactly two constant instances: True and False.

.. index:: single: False single: True pair: Boolean; values

The built-in function :func:bool converts any value to a boolean, if the value can be interpreted as a truth value (see section :ref:truth above).

For logical operations, use the :ref:boolean operators <boolean> and, or and not. When applying the bitwise operators &, |, ^ to two booleans, they return a bool equivalent to the logical operations "and", "or", "xor". However, the logical operators and, or and != should be preferred over &, | and ^.

.. deprecated:: 3.12

The use of the bitwise inversion operator ~ is deprecated and will raise an error in Python 3.16.

:class:bool is a subclass of :class:int (see :ref:typesnumeric). In many numeric contexts, False and True behave like the integers 0 and 1, respectively. However, relying on this is discouraged; explicitly convert using :func:int instead.

.. _typeiter:

Iterator Types

.. index:: single: iterator protocol single: protocol; iterator single: sequence; iteration single: container; iteration over

Python supports a concept of iteration over containers. This is implemented using two distinct methods; these are used to allow user-defined classes to support iteration. Sequences, described below in more detail, always support the iteration methods.

One method needs to be defined for container objects to provide :term:iterable support:

.. XXX duplicated in reference/datamodel!

.. method:: container.iter()

Return an :term:iterator object. The object is required to support the iterator protocol described below. If a container supports different types of iteration, additional methods can be provided to specifically request iterators for those iteration types. (An example of an object supporting multiple forms of iteration would be a tree structure which supports both breadth-first and depth-first traversal.) This method corresponds to the :c:member:~PyTypeObject.tp_iter slot of the type structure for Python objects in the Python/C API.

The iterator objects themselves are required to support the following two methods, which together form the :dfn:iterator protocol:

.. method:: iterator.iter()

Return the :term:iterator object itself. This is required to allow both containers and iterators to be used with the :keyword:for and :keyword:in statements. This method corresponds to the :c:member:~PyTypeObject.tp_iter slot of the type structure for Python objects in the Python/C API.

.. method:: iterator.next()

Return the next item from the :term:iterator. If there are no further items, raise the :exc:StopIteration exception. This method corresponds to the :c:member:~PyTypeObject.tp_iternext slot of the type structure for Python objects in the Python/C API.

Python defines several iterator objects to support iteration over general and specific sequence types, dictionaries, and other more specialized forms. The specific types are not important beyond their implementation of the iterator protocol.

Once an iterator's :meth:~iterator.__next__ method raises :exc:StopIteration, it must continue to do so on subsequent calls. Implementations that do not obey this property are deemed broken.

.. _generator-types:

Generator Types

Python's :term:generator\s provide a convenient way to implement the iterator protocol. If a container object's :meth:~object.__iter__ method is implemented as a generator, it will automatically return an iterator object (technically, a generator object) supplying the :meth:~iterator.__iter__ and :meth:~generator.__next__ methods. More information about generators can be found in :ref:the documentation for the yield expression <yieldexpr>.

.. _typesseq:

Sequence Types --- :class:`list`, :class:`tuple`, :class:`range`

There are three basic sequence types: lists, tuples, and range objects. Additional sequence types tailored for processing of :ref:binary data <binaryseq> and :ref:text strings <textseq> are described in dedicated sections.

.. _typesseq-common:

Common Sequence Operations

.. index:: pair: object; sequence

The operations in the following table are supported by most sequence types, both mutable and immutable. The :class:collections.abc.Sequence ABC is provided to make it easier to correctly implement these operations on custom sequence types.

This table lists the sequence operations sorted in ascending priority. In the table, s and t are sequences of the same type, n, i, j and k are integers and x is an arbitrary object that meets any type and value restrictions imposed by s.

The in and not in operations have the same priorities as the comparison operations. The + (concatenation) and * (repetition) operations have the same priority as the corresponding numeric operations. [3]_

.. index:: triple: operations on; sequence; types pair: built-in function; len pair: built-in function; min pair: built-in function; max pair: concatenation; operation pair: repetition; operation pair: subscript; operation pair: slice; operation pair: operator; in pair: operator; not in

+--------------------------+--------------------------------+----------+ | Operation | Result | Notes | +==========================+================================+==========+ | x in s | True if an item of s is | (1) | | | equal to x, else False | | +--------------------------+--------------------------------+----------+ | x not in s | False if an item of s is | (1) | | | equal to x, else True | | +--------------------------+--------------------------------+----------+ | s + t | the concatenation of s and | (6)(7) | | | t | | +--------------------------+--------------------------------+----------+ | s * n or | equivalent to adding s to | (2)(7) | | n * s | itself n times | | +--------------------------+--------------------------------+----------+ | s[i] | i\ th item of s, origin 0 | (3)(8) | +--------------------------+--------------------------------+----------+ | s[i:j] | slice of s from i to j | (3)(4) | +--------------------------+--------------------------------+----------+ | s[i:j:k] | slice of s from i to j | (3)(5) | | | with step k | | +--------------------------+--------------------------------+----------+ | len(s) | length of s | | +--------------------------+--------------------------------+----------+ | min(s) | smallest item of s | | +--------------------------+--------------------------------+----------+ | max(s) | largest item of s | | +--------------------------+--------------------------------+----------+

Sequences of the same type also support comparisons. In particular, tuples and lists are compared lexicographically by comparing corresponding elements. This means that to compare equal, every element must compare equal and the two sequences must be of the same type and have the same length. (For full details see :ref:comparisons in the language reference.)

.. index:: single: loop; over mutable sequence single: mutable sequence; loop over

Forward and reversed iterators over mutable sequences access values using an index. That index will continue to march forward (or backward) even if the underlying sequence is mutated. The iterator terminates only when an :exc:IndexError or a :exc:StopIteration is encountered (or when the index drops below zero).

Notes:

(1) While the in and not in operations are used only for simple containment testing in the general case, some specialised sequences (such as :class:str, :class:bytes and :class:bytearray) also use them for subsequence testing::

  >>> "gg" in "eggs"
  True

(2) Values of n less than 0 are treated as 0 (which yields an empty sequence of the same type as s). Note that items in the sequence s are not copied; they are referenced multiple times. This often haunts new Python programmers; consider::

  >>> lists = [[]] * 3
  >>> lists
  [[], [], []]
  >>> lists[0].append(3)
  >>> lists
  [[3], [3], [3]]

What has happened is that [[]] is a one-element list containing an empty list, so all three elements of [[]] * 3 are references to this single empty list. Modifying any of the elements of lists modifies this single list. You can create a list of different lists this way::

  >>> lists = [[] for i in range(3)]
  >>> lists[0].append(3)
  >>> lists[1].append(5)
  >>> lists[2].append(7)
  >>> lists
  [[3], [5], [7]]

Further explanation is available in the FAQ entry :ref:faq-multidimensional-list.

(3) If i or j is negative, the index is relative to the end of sequence s: len(s) + i or len(s) + j is substituted. But note that -0 is still 0.

(4) The slice of s from i to j is defined as the sequence of items with index k such that i <= k < j.

If i is omitted or None, use 0.
If j is omitted or None, use len(s).
If i or j is less than -len(s), use 0.
If i or j is greater than len(s), use len(s).
If i is greater than or equal to j, the slice is empty.

(5) The slice of s from i to j with step k is defined as the sequence of items with index x = i + n*k such that 0 <= n < (j-i)/k. In other words, the indices are i, i+k, i+2*k, i+3*k and so on, stopping when j is reached (but never including j). When k is positive, i and j are reduced to len(s) if they are greater. When k is negative, i and j are reduced to len(s) - 1 if they are greater. If i or j are omitted or None, they become "end" values (which end depends on the sign of k). Note, k cannot be zero. If k is None, it is treated like 1.

(6) Concatenating immutable sequences always results in a new object. This means that building up a sequence by repeated concatenation will have a quadratic runtime cost in the total sequence length. To get a linear runtime cost, you must switch to one of the alternatives below:

if concatenating :class:str objects, you can build a list and use :meth:str.join at the end or else write to an :class:io.StringIO instance and retrieve its value when complete
if concatenating :class:bytes objects, you can similarly use :meth:bytes.join or :class:io.BytesIO, or you can do in-place concatenation with a :class:bytearray object. :class:bytearray objects are mutable and have an efficient overallocation mechanism
if concatenating :class:tuple objects, extend a :class:list instead
for other types, investigate the relevant class documentation

(7) Some sequence types (such as :class:range) only support item sequences that follow specific patterns, and hence don't support sequence concatenation or repetition.

(8) An :exc:IndexError is raised if i is outside the sequence range.

.. rubric:: Sequence Methods

Sequence types also support the following methods:

.. method:: list.count(value, /) range.count(value, /) tuple.count(value, /) :no-contents-entry: :no-index-entry: :no-typesetting: .. method:: sequence.count(value, /)

Return the total number of occurrences of value in sequence.

.. method:: list.index(value[, start[, stop]]) range.index(value[, start[, stop]]) tuple.index(value[, start[, stop]]) :no-contents-entry: :no-index-entry: :no-typesetting: .. method:: sequence.index(value[, start[, stop]])

Return the index of the first occurrence of value in sequence.

Raises :exc:ValueError if value is not found in sequence.

The start or stop arguments allow for efficient searching of subsections of the sequence, beginning at start and ending at stop. This is roughly equivalent to start + sequence[start:stop].index(value), only without copying any data.

.. caution:: Not all sequence types support passing the start and stop arguments.

.. _typesseq-immutable:

Immutable Sequence Types

.. index:: triple: immutable; sequence; types pair: object; tuple pair: built-in function; hash

The only operation that immutable sequence types generally implement that is not also implemented by mutable sequence types is support for the :func:hash built-in.

This support allows immutable sequences, such as :class:tuple instances, to be used as :class:dict keys and stored in :class:set and :class:frozenset instances.

Attempting to hash an immutable sequence that contains unhashable values will result in :exc:TypeError.

.. _typesseq-mutable:

Mutable Sequence Types

.. index:: triple: mutable; sequence; types pair: object; list pair: object; bytearray

The operations in the following table are defined on mutable sequence types. The :class:collections.abc.MutableSequence ABC is provided to make it easier to correctly implement these operations on custom sequence types.

In the table s is an instance of a mutable sequence type, t is any iterable object and x is an arbitrary object that meets any type and value restrictions imposed by s (for example, :class:bytearray only accepts integers that meet the value restriction 0 <= x <= 255).

.. index:: triple: operations on; sequence; types triple: operations on; list; type pair: subscript; assignment pair: slice; assignment pair: statement; del

Notes:

(1) If k is not equal to 1, t must have the same length as the slice it is replacing.

(2) The value n is an integer, or an object implementing :meth:~object.__index__. Zero and negative values of n clear the sequence. Items in the sequence are not copied; they are referenced multiple times, as explained for s * n under :ref:typesseq-common.

.. rubric:: Mutable Sequence Methods

Mutable sequence types also support the following methods:

.. method:: bytearray.append(value, /) list.append(value, /) :no-contents-entry: :no-index-entry: :no-typesetting: .. method:: sequence.append(value, /)

Append value to the end of the sequence. This is equivalent to writing seq[len(seq):len(seq)] = [value].

.. method:: bytearray.clear() list.clear() :no-contents-entry: :no-index-entry: :no-typesetting: .. method:: sequence.clear()

.. versionadded:: 3.3

Remove all items from sequence. This is equivalent to writing del sequence[:].

.. method:: bytearray.copy() list.copy() :no-contents-entry: :no-index-entry: :no-typesetting: .. method:: sequence.copy()

.. versionadded:: 3.3

Create a shallow copy of sequence. This is equivalent to writing sequence[:].

.. hint:: The :meth:!copy method is not part of the :class:~collections.abc.MutableSequence :class:~abc.ABC, but most concrete mutable sequence types provide it.

.. method:: bytearray.extend(iterable, /) list.extend(iterable, /) :no-contents-entry: :no-index-entry: :no-typesetting: .. method:: sequence.extend(iterable, /)

Extend sequence with the contents of iterable. For the most part, this is the same as writing seq[len(seq):len(seq)] = iterable.

.. method:: bytearray.insert(index, value, /) list.insert(index, value, /) :no-contents-entry: :no-index-entry: :no-typesetting: .. method:: sequence.insert(index, value, /)

Insert value into sequence at the given index. This is equivalent to writing sequence[index:index] = [value].

.. method:: bytearray.pop(index=-1, /) list.pop(index=-1, /) :no-contents-entry: :no-index-entry: :no-typesetting: .. method:: sequence.pop(index=-1, /)

Retrieve the item at index and also removes it from sequence. By default, the last item in sequence is removed and returned.

.. method:: bytearray.remove(value, /) list.remove(value, /) :no-contents-entry: :no-index-entry: :no-typesetting: .. method:: sequence.remove(value, /)

Remove the first item from sequence where sequence[i] == value.

Raises :exc:ValueError if value is not found in sequence.

.. method:: bytearray.reverse() list.reverse() :no-contents-entry: :no-index-entry: :no-typesetting: .. method:: sequence.reverse()

Reverse the items of sequence in place. This method maintains economy of space when reversing a large sequence. To remind users that it operates by side-effect, it returns None.

.. _typesseq-list:

Lists

.. index:: pair: object; list

Lists are mutable sequences, typically used to store collections of homogeneous items (where the precise degree of similarity will vary by application).

.. class:: list(iterable=(), /)

Lists may be constructed in several ways:

Using a pair of square brackets to denote the empty list: []
Using square brackets, separating items with commas: [a], [a, b, c]
Using a list comprehension: [x for x in iterable]
Using the type constructor: list() or list(iterable)

The constructor builds a list whose items are the same and in the same order as iterable's items. iterable may be either a sequence, a container that supports iteration, or an iterator object. If iterable is already a list, a copy is made and returned, similar to iterable[:]. For example, list('abc') returns ['a', 'b', 'c'] and list( (1, 2, 3) ) returns [1, 2, 3]. If no argument is given, the constructor creates a new empty list, [].

Many other operations also produce lists, including the :func:sorted built-in.

Lists implement all of the :ref:common <typesseq-common> and :ref:mutable <typesseq-mutable> sequence operations. Lists also provide the following additional method:

.. method:: list.sort(*, key=None, reverse=False)

  This method sorts the list in place, using only ``<`` comparisons
  between items. Exceptions are not suppressed - if any comparison operations
  fail, the entire sort operation will fail (and the list will likely be left
  in a partially modified state).

  :meth:`sort` accepts two arguments that can only be passed by keyword
  (:ref:`keyword-only arguments <keyword-only_parameter>`):

  *key* specifies a function of one argument that is used to extract a
  comparison key from each list element (for example, ``key=str.lower``).
  The key corresponding to each item in the list is calculated once and
  then used for the entire sorting process. The default value of ``None``
  means that list items are sorted directly without calculating a separate
  key value.

  The :func:`functools.cmp_to_key` utility is available to convert a 2.x
  style *cmp* function to a *key* function.

  *reverse* is a boolean value.  If set to ``True``, then the list elements
  are sorted as if each comparison were reversed.

  This method modifies the sequence in place for economy of space when
  sorting a large sequence.  To remind users that it operates by side
  effect, it does not return the sorted sequence (use :func:`sorted` to
  explicitly request a new sorted list instance).

  The :meth:`sort` method is guaranteed to be stable.  A sort is stable if it
  guarantees not to change the relative order of elements that compare equal
  --- this is helpful for sorting in multiple passes (for example, sort by
  department, then by salary grade).

  For sorting examples and a brief sorting tutorial, see :ref:`sortinghowto`.

  .. impl-detail::

     While a list is being sorted, the effect of attempting to mutate, or even
     inspect, the list is undefined.  The C implementation of Python makes the
     list appear empty for the duration, and raises :exc:`ValueError` if it can
     detect that the list has been mutated during a sort.

.. seealso::

For detailed information on thread-safety guarantees for :class:list objects, see :ref:thread-safety-list.

.. _typesseq-tuple:

Tuples

.. index:: pair: object; tuple

Tuples are immutable sequences, typically used to store collections of heterogeneous data (such as the 2-tuples produced by the :func:enumerate built-in). Tuples are also used for cases where an immutable sequence of homogeneous data is needed (such as allowing storage in a :class:set or :class:dict instance).

.. class:: tuple(iterable=(), /)

Tuples may be constructed in a number of ways:

Using a pair of parentheses to denote the empty tuple: ()
Using a trailing comma for a singleton tuple: a, or (a,)
Separating items with commas: a, b, c or (a, b, c)
Using the :func:tuple built-in: tuple() or tuple(iterable)

The constructor builds a tuple whose items are the same and in the same order as iterable's items. iterable may be either a sequence, a container that supports iteration, or an iterator object. If iterable is already a tuple, it is returned unchanged. For example, tuple('abc') returns ('a', 'b', 'c') and tuple( [1, 2, 3] ) returns (1, 2, 3). If no argument is given, the constructor creates a new empty tuple, ().

Note that it is actually the comma which makes a tuple, not the parentheses. The parentheses are optional, except in the empty tuple case, or when they are needed to avoid syntactic ambiguity. For example, f(a, b, c) is a function call with three arguments, while f((a, b, c)) is a function call with a 3-tuple as the sole argument.

Tuples implement all of the :ref:common <typesseq-common> sequence operations.

For heterogeneous collections of data where access by name is clearer than access by index, :func:collections.namedtuple may be a more appropriate choice than a simple tuple object.

.. _typesseq-range:

Ranges

.. index:: pair: object; range

The :class:range type represents an immutable sequence of numbers and is commonly used for looping a specific number of times in :keyword:for loops.

.. class:: range(stop, /) range(start, stop, step=1, /)

The arguments to the range constructor must be integers (either built-in :class:int or any object that implements the :meth:~object.__index__ special method). If the step argument is omitted, it defaults to 1. If the start argument is omitted, it defaults to 0. If step is zero, :exc:ValueError is raised.

For a positive step, the contents of a range r are determined by the formula r[i] = start + step*i where i >= 0 and r[i] < stop.

For a negative step, the contents of the range are still determined by the formula r[i] = start + step*i, but the constraints are i >= 0 and r[i] > stop.

A range object will be empty if r[0] does not meet the value constraint. Ranges do support negative indices, but these are interpreted as indexing from the end of the sequence determined by the positive indices.

Ranges containing absolute values larger than :data:sys.maxsize are permitted but some features (such as :func:len) may raise :exc:OverflowError.

Range examples::

  >>> list(range(10))
  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  >>> list(range(1, 11))
  [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  >>> list(range(0, 30, 5))
  [0, 5, 10, 15, 20, 25]
  >>> list(range(0, 10, 3))
  [0, 3, 6, 9]
  >>> list(range(0, -10, -1))
  [0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
  >>> list(range(0))
  []
  >>> list(range(1, 0))
  []

Ranges implement all of the :ref:common <typesseq-common> sequence operations except concatenation and repetition (due to the fact that range objects can only represent sequences that follow a strict pattern and repetition and concatenation will usually violate that pattern).

.. attribute:: start

  The value of the *start* parameter (or ``0`` if the parameter was
  not supplied)

.. attribute:: stop

  The value of the *stop* parameter

.. attribute:: step

  The value of the *step* parameter (or ``1`` if the parameter was
  not supplied)

The advantage of the :class:range type over a regular :class:list or :class:tuple is that a :class:range object will always take the same (small) amount of memory, no matter the size of the range it represents (as it only stores the start, stop and step values, calculating individual items and subranges as needed).

Range objects implement the :class:collections.abc.Sequence ABC, and provide features such as containment tests, element index lookup, slicing and support for negative indices (see :ref:typesseq):

r = range(0, 20, 2) r range(0, 20, 2) 11 in r False 10 in r True r.index(10) 5 r[5] 10 r[:5] range(0, 10, 2) r[-1] 18

Testing range objects for equality with == and != compares them as sequences. That is, two range objects are considered equal if they represent the same sequence of values. (Note that two range objects that compare equal might have different :attr:~range.start, :attr:~range.stop and :attr:~range.step attributes, for example range(0) == range(2, 1, 3) or range(0, 3, 2) == range(0, 4, 2).)

.. versionchanged:: 3.2 Implement the Sequence ABC. Support slicing and negative indices. Test :class:int objects for membership in constant time instead of iterating through all items.

.. versionchanged:: 3.3 Define '==' and '!=' to compare range objects based on the sequence of values they define (instead of comparing based on object identity).

Added the :attr:~range.start, :attr:~range.stop and :attr:~range.step attributes.

.. seealso::

The linspace recipe <https://code.activestate.com/recipes/579000-equally-spaced-numbers-linspace/>_ shows how to implement a lazy version of range suitable for floating-point applications.

.. index:: single: string; text sequence type single: str (built-in class); (see also string) pair: object; string

.. _text-methods-summary:

Text and Binary Sequence Type Methods Summary

The following table summarizes the text and binary sequence types methods by category.

+--------------------------+-------------------------------------------+---------------------------------------------------+ | Category | :class:str methods | :class:bytes and :class:bytearray methods | +==========================+===========================================+===================================================+ | Formatting | :meth:str.format | | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.format_map | | | +-------------------------------------------+---------------------------------------------------+ | | :ref:f-strings | | | +-------------------------------------------+---------------------------------------------------+ | | :ref:old-string-formatting | :ref:bytes-formatting | +--------------------------+------------------+------------------------+--------------------+------------------------------+ | Searching and Replacing | :meth:str.find | :meth:str.rfind | :meth:bytes.find | :meth:bytes.rfind | | +------------------+------------------------+--------------------+------------------------------+ | | :meth:str.index| :meth:str.rindex | :meth:bytes.index| :meth:bytes.rindex | | +------------------+------------------------+--------------------+------------------------------+ | | :meth:str.startswith | :meth:bytes.startswith | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.endswith | :meth:bytes.endswith | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.count | :meth:bytes.count | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.replace | :meth:bytes.replace | +--------------------------+-------------------+-----------------------+---------------------+-----------------------------+ | Splitting and Joining | :meth:str.split | :meth:str.rsplit | :meth:bytes.split | :meth:bytes.rsplit | | +-------------------+-----------------------+---------------------+-----------------------------+ | | :meth:str.splitlines | :meth:bytes.splitlines | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.partition | :meth:bytes.partition | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.rpartition | :meth:bytes.rpartition | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.join | :meth:bytes.join | +--------------------------+-------------------------------------------+---------------------------------------------------+ | String Classification | :meth:str.isalpha | :meth:bytes.isalpha | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.isdecimal | | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.isdigit | :meth:bytes.isdigit | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.isnumeric | | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.isalnum | :meth:bytes.isalnum | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.isidentifier | | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.islower | :meth:bytes.islower | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.isupper | :meth:bytes.isupper | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.istitle | :meth:bytes.istitle | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.isspace | :meth:bytes.isspace | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.isprintable | | +--------------------------+-------------------------------------------+---------------------------------------------------+ | Case Manipulation | :meth:str.lower | :meth:bytes.lower | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.upper | :meth:bytes.upper | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.casefold | | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.capitalize | :meth:bytes.capitalize | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.title | :meth:bytes.title | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.swapcase | :meth:bytes.swapcase | +--------------------------+-------------------+-----------------------+---------------------+-----------------------------+ | Padding and Stripping | :meth:str.ljust | :meth:str.rjust | :meth:bytes.ljust | :meth:bytes.rjust | | +-------------------+-----------------------+---------------------+-----------------------------+ | | :meth:str.center | :meth:bytes.center | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.expandtabs | :meth:bytes.expandtabs | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.strip | :meth:bytes.strip | | +--------------------+----------------------+----------------------+----------------------------+ | | :meth:str.lstrip | :meth:str.rstrip | :meth:bytes.lstrip | :meth:bytes.rstrip | +--------------------------+--------------------+----------------------+----------------------+----------------------------+ | Translation and Encoding | :meth:str.translate | :meth:bytes.translate | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.maketrans | :meth:bytes.maketrans | | +-------------------------------------------+---------------------------------------------------+ | | :meth:str.encode | | | +-------------------------------------------+---------------------------------------------------+ | | | :meth:bytes.decode | +--------------------------+-------------------------------------------+---------------------------------------------------+

.. _textseq:

Text Sequence Type --- :class:`str`

Textual data in Python is handled with :class:str objects, or :dfn:strings. Strings are immutable :ref:sequences <typesseq> of Unicode code points. String literals are written in a variety of ways:

Single quotes: 'allows embedded "double" quotes'
Double quotes: "allows embedded 'single' quotes"
Triple quoted: '''Three single quotes''', """Three double quotes"""

Triple quoted strings may span multiple lines - all associated whitespace will be included in the string literal.

String literals that are part of a single expression and have only whitespace between them will be implicitly converted to a single string literal. That is, ("spam " "eggs") == "spam eggs".

See :ref:strings for more about the various forms of string literal, including supported :ref:escape sequences <escape-sequences>, and the r ("raw") prefix that disables most escape sequence processing.

Strings may also be created from other objects using the :class:str constructor.

Since there is no separate "character" type, indexing a string produces strings of length 1. That is, for a non-empty string s, s[0] == s[0:1].

.. index:: pair: object; io.StringIO

There is also no mutable string type, but :meth:str.join or :class:io.StringIO can be used to efficiently construct strings from multiple fragments.

.. versionchanged:: 3.3 For backwards compatibility with the Python 2 series, the u prefix is once again permitted on string literals. It has no effect on the meaning of string literals and cannot be combined with the r prefix.

.. index:: single: string; str (built-in class)

.. class:: str(*, encoding='utf-8', errors='strict') str(object) str(object, encoding, errors='strict') str(object, *, errors)

Return a :ref:string <textseq> version of object. If object is not provided, returns the empty string. Otherwise, the behavior of str() depends on whether encoding or errors is given, as follows.

If neither encoding nor errors is given, str(object) returns :meth:type(object).__str__(object) <object.__str__>, which is the "informal" or nicely printable string representation of object. For string objects, this is the string itself. If object does not have a :meth:~object.__str__ method, then :func:str falls back to returning :func:repr(object) <repr>.

.. index:: single: buffer protocol; str (built-in class) single: bytes; str (built-in class)

If at least one of encoding or errors is given, object should be a :term:bytes-like object (e.g. :class:bytes or :class:bytearray). In this case, if object is a :class:bytes (or :class:bytearray) object, then str(bytes, encoding, errors) is equivalent to :meth:bytes.decode(encoding, errors) <bytes.decode>. Otherwise, the bytes object underlying the buffer object is obtained before calling :meth:bytes.decode. See :ref:binaryseq and :ref:bufferobjects for information on buffer objects.

Passing a :class:bytes object to :func:str without the encoding or errors arguments falls under the first case of returning the informal string representation (see also the :option:-b command-line option to Python). For example::

  >>> str(b'Zoot!')
  "b'Zoot!'"

For more information on the str class and its methods, see :ref:textseq and the :ref:string-methods section below. To output formatted strings, see the :ref:f-strings and :ref:formatstrings sections. In addition, see the :ref:stringservices section.

.. index:: pair: string; methods

.. _string-methods:

String Methods

.. index:: pair: module; re

Strings implement all of the :ref:common <typesseq-common> sequence operations, along with the additional methods described below.

Strings also support two styles of string formatting, one providing a large degree of flexibility and customization (see :meth:str.format, :ref:formatstrings and :ref:string-formatting) and the other based on C printf style formatting that handles a narrower range of types and is slightly harder to use correctly, but is often faster for the cases it can handle (:ref:old-string-formatting).

The :ref:textservices section of the standard library covers a number of other modules that provide various text related utilities (including regular expression support in the :mod:re module).

.. method:: str.capitalize()

Return a copy of the string with its first character capitalized and the rest lowercased.

.. versionchanged:: 3.8 The first character is now put into titlecase rather than uppercase. This means that characters like digraphs will only have their first letter capitalized, instead of the full character.

.. method:: str.casefold()

Return a casefolded copy of the string. Casefolded strings may be used for caseless matching.

Casefolding is similar to lowercasing but more aggressive because it is intended to remove all case distinctions in a string. For example, the German lowercase letter 'ß' is equivalent to "ss". Since it is already lowercase, :meth:lower would do nothing to 'ß'; :meth:casefold converts it to "ss". For example:

.. doctest::

  >>> 'straße'.lower()
  'straße'
  >>> 'straße'.casefold()
  'strasse'

The casefolding algorithm is described in section 3.13.3 'Default Case Folding' of the Unicode Standard <https://www.unicode.org/versions/Unicode17.0.0/core-spec/chapter-3/#G53253>__.

.. versionadded:: 3.3

.. method:: str.center(width, fillchar=' ', /)

Return centered in a string of length width. Padding is done using the specified fillchar (default is an ASCII space). The original string is returned if width is less than or equal to len(s). For example::

  >>> 'Python'.center(10)
  '  Python  '
  >>> 'Python'.center(10, '-')
  '--Python--'
  >>> 'Python'.center(4)
  'Python'

.. method:: str.count(sub[, start[, end]])

Return the number of non-overlapping occurrences of substring sub in the range [start, end]. Optional arguments start and end are interpreted as in slice notation.

If sub is empty, returns the number of empty strings between characters which is the length of the string plus one. For example::

  >>> 'spam, spam, spam'.count('spam')
  3
  >>> 'spam, spam, spam'.count('spam', 5)
  2
  >>> 'spam, spam, spam'.count('spam', 5, 10)
  1
  >>> 'spam, spam, spam'.count('eggs')
  0
  >>> 'spam, spam, spam'.count('')
  17

.. method:: str.encode(encoding="utf-8", errors="strict")

Return the string encoded to :class:bytes.

encoding defaults to 'utf-8'; see :ref:standard-encodings for possible values.

errors controls how encoding errors are handled. If 'strict' (the default), a :exc:UnicodeError exception is raised. Other possible values are 'ignore', 'replace', 'xmlcharrefreplace', 'backslashreplace' and any other name registered via :func:codecs.register_error. See :ref:error-handlers for details.

For performance reasons, the value of errors is not checked for validity unless an encoding error actually occurs, :ref:devmode is enabled or a :ref:debug build <debug-build> is used. For example::

  >>> encoded_str_to_bytes = 'Python'.encode()
  >>> type(encoded_str_to_bytes)
  <class 'bytes'>
  >>> encoded_str_to_bytes
  b'Python'

.. versionchanged:: 3.1 Added support for keyword arguments.

.. versionchanged:: 3.9 The value of the errors argument is now checked in :ref:devmode and in :ref:debug mode <debug-build>.

.. method:: str.endswith(suffix[, start[, end]])

Return True if the string ends with the specified suffix, otherwise return False. suffix can also be a tuple of suffixes to look for. With optional start, test beginning at that position. With optional end, stop comparing at that position. Using start and end is equivalent to str[start:end].endswith(suffix). For example::

  >>> 'Python'.endswith('on')
  True
  >>> 'a tuple of suffixes'.endswith(('at', 'in'))
  False
  >>> 'a tuple of suffixes'.endswith(('at', 'es'))
  True
  >>> 'Python is amazing'.endswith('is', 0, 9)
  True

See also :meth:startswith and :meth:removesuffix.

.. method:: str.expandtabs(tabsize=8)

Return a copy of the string where all tab characters are replaced by one or more spaces, depending on the current column and the given tab size. Tab positions occur every tabsize characters (default is 8, giving tab positions at columns 0, 8, 16 and so on). To expand the string, the current column is set to zero and the string is examined character by character. If the character is a tab (\t), one or more space characters are inserted in the result until the current column is equal to the next tab position. (The tab character itself is not copied.) If the character is a newline (\n) or return (\r), it is copied and the current column is reset to zero. Any other character is copied unchanged and the current column is incremented by one regardless of how the character is represented when printed. For example::

  >>> '01\t012\t0123\t01234'.expandtabs()
  '01      012     0123    01234'
  >>> '01\t012\t0123\t01234'.expandtabs(4)
  '01  012 0123    01234'
  >>> print('01\t012\n0123\t01234'.expandtabs(4))
  01  012
  0123    01234

.. method:: str.find(sub[, start[, end]])

Return the lowest index in the string where substring sub is found within the slice s[start:end]. Optional arguments start and end are interpreted as in slice notation. Return -1 if sub is not found. For example::

  >>> 'spam, spam, spam'.find('sp')
  0
  >>> 'spam, spam, spam'.find('sp', 5)
  6

See also :meth:rfind and :meth:index.

.. note::

  The :meth:`~str.find` method should be used only if you need to know the
  position of *sub*.  To check if *sub* is a substring or not, use the
  :keyword:`in` operator::

     >>> 'Py' in 'Python'
     True

.. method:: str.format(*args, **kwargs)

Perform a string formatting operation. The string on which this method is called can contain literal text or replacement fields delimited by braces {}. Each replacement field contains either the numeric index of a positional argument, or the name of a keyword argument. Returns a copy of the string where each replacement field is replaced with the string value of the corresponding argument. For example:

.. doctest::

  >>> "The sum of 1 + 2 is {0}".format(1+2)
  'The sum of 1 + 2 is 3'
  >>> "The sum of {a} + {b} is {answer}".format(answer=1+2, a=1, b=2)
  'The sum of 1 + 2 is 3'
  >>> "{1} expects the {0} Inquisition!".format("Spanish", "Nobody")
  'Nobody expects the Spanish Inquisition!'

See :ref:formatstrings for a description of the various formatting options that can be specified in format strings.

.. note:: When formatting a number (:class:int, :class:float, :class:complex, :class:decimal.Decimal and subclasses) with the n type (ex: '{:n}'.format(1234)), the function temporarily sets the LC_CTYPE locale to the LC_NUMERIC locale to decode decimal_point and thousands_sep fields of :c:func:localeconv if they are non-ASCII or longer than 1 byte, and the LC_NUMERIC locale is different than the LC_CTYPE locale. This temporary change affects other threads.

.. versionchanged:: 3.7 When formatting a number with the n type, the function sets temporarily the LC_CTYPE locale to the LC_NUMERIC locale in some cases.

.. method:: str.format_map(mapping, /)

Similar to str.format(**mapping), except that mapping is used directly and not copied to a :class:dict. This is useful if for example mapping is a dict subclass:

class Default(dict): ... def missing(self, key): ... return key ... '{name} was born in {country}'.format_map(Default(name='Guido')) 'Guido was born in country'

.. versionadded:: 3.2

.. method:: str.index(sub[, start[, end]])

Like :meth:~str.find, but raise :exc:ValueError when the substring is not found. For example:

.. doctest::

  >>> 'spam, spam, spam'.index('spam')
  0
  >>> 'spam, spam, spam'.index('eggs')
  Traceback (most recent call last):
    File "<python-input-0>", line 1, in <module>
      'spam, spam, spam'.index('eggs')
      ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^
  ValueError: substring not found

Formatted String Literals (f-strings)

.. versionadded:: 3.6 .. versionchanged:: 3.7 The :keyword:await and :keyword:async for can be used in expressions within f-strings. .. versionchanged:: 3.8 Added the debug specifier (=) .. versionchanged:: 3.12 Many restrictions on expressions within f-strings have been removed. Notably, nested strings, comments, and backslashes are now permitted.

An :dfn:f-string (formally a :dfn:formatted string literal) is a string literal that is prefixed with f or F. This type of string literal allows embedding the results of arbitrary Python expressions within replacement fields, which are delimited by curly brackets ({}). Each replacement field must contain an expression, optionally followed by:

a debug specifier -- an equal sign (=);
a conversion specifier -- !s, !r or !a; and/or
a format specifier prefixed with a colon (:).

See the :ref:Lexical Analysis section on f-strings <f-strings> for details on the syntax of these fields.

Debug specifier ^^^^^^^^^^^^^^^

.. versionadded:: 3.8

If a debug specifier -- an equal sign (=) -- appears after the replacement field expression, the resulting f-string will contain the expression's source, the equal sign, and the value of the expression. This is often useful for debugging::

number = 14.3 f'{number=}' 'number=14.3'

Whitespace before, inside and after the expression, as well as whitespace after the equal sign, is significant --- it is retained in the result::

f'{ number - 4 = }' ' number - 4 = 10.3'

Conversion specifier ^^^^^^^^^^^^^^^^^^^^

By default, the value of a replacement field expression is converted to a string using :func:str::

from fractions import Fraction one_third = Fraction(1, 3) f'{one_third}' '1/3'

When a debug specifier but no format specifier is used, the default conversion instead uses :func:repr::

f'{one_third = }' 'one_third = Fraction(1, 3)'

The conversion can be specified explicitly using one of these specifiers:

!s for :func:str
!r for :func:repr
!a for :func:ascii

For example::

str(one_third) '1/3' repr(one_third) 'Fraction(1, 3)'

f'{one_third!s} is {one_third!r}' '1/3 is Fraction(1, 3)'

string = "¡kočka 😸!" ascii(string) "'\xa1ko\u010dka \U0001f638!'"

f'{string = !a}' "string = '\xa1ko\u010dka \U0001f638!'"

Format specifier ^^^^^^^^^^^^^^^^

After the expression has been evaluated, and possibly converted using an explicit conversion specifier, it is formatted using the :func:format function. If the replacement field includes a format specifier introduced by a colon (:), the specifier is passed to :func:!format as the second argument. The result of :func:!format is then used as the final value for the replacement field. For example::

from fractions import Fraction one_third = Fraction(1, 3) f'{one_third:.6f}' '0.333333' f'{one_third:^+10}' '+1/3_'

f'{one_third!r:_^20}' 'Fraction(1, 3)' f'{one_third = :~~>10}~~' 'one_third = ~~~~~~~1/3~'

.. _stdtypes-tstrings:

Template String Literals (t-strings)

An :dfn:t-string (formally a :dfn:template string literal) is a string literal that is prefixed with t or T.

These strings follow the same syntax and evaluation rules as :ref:formatted string literals <stdtypes-fstrings>, with for the following differences:

Rather than evaluating to a str object, template string literals evaluate to a :class:string.templatelib.Template object.
The :func:format protocol is not used. Instead, the format specifier and conversions (if any) are passed to a new :class:~string.templatelib.Interpolation object that is created for each evaluated expression. It is up to code that processes the resulting :class:~string.templatelib.Template object to decide how to handle format specifiers and conversions.
Format specifiers containing nested replacement fields are evaluated eagerly, prior to being passed to the :class:~string.templatelib.Interpolation object. For instance, an interpolation of the form {amount:.{precision}f} will evaluate the inner expression {precision} to determine the value of the format_spec attribute. If precision were to be 2, the resulting format specifier would be '.2f'.
When the equals sign '=' is provided in an interpolation expression, the text of the expression is appended to the literal string that precedes the relevant interpolation. This includes the equals sign and any surrounding whitespace. The :class:!Interpolation instance for the expression will be created as normal, except that :attr:~string.templatelib.Interpolation.conversion will be set to 'r' (:func:repr) by default. If an explicit conversion or format specifier are provided, this will override the default behaviour.

.. _old-string-formatting:

`printf`-style String Formatting

.. index:: single: formatting, string (%) single: interpolation, string (%) single: string; formatting, printf single: string; interpolation, printf single: printf-style formatting single: sprintf-style formatting single: % (percent); printf-style formatting

.. note::

The formatting operations described here exhibit a variety of quirks that lead to a number of common errors (such as failing to display tuples and dictionaries correctly).

Using :ref:formatted string literals <f-strings>, the :meth:str.format interface, or :class:string.Template may help avoid these errors. Each of these alternatives provides their own trade-offs and benefits of simplicity, flexibility, and/or extensibility.

String objects have one unique built-in operation: the % operator (modulo). This is also known as the string formatting or interpolation operator. Given format % values (where format is a string), % conversion specifications in format are replaced with zero or more elements of values. The effect is similar to using the :c:func:sprintf function in the C language. For example:

.. doctest::

print('%s has %d quote types.' % ('Python', 2)) Python has 2 quote types.

If format requires a single argument, values may be a single non-tuple object. [5]_ Otherwise, values must be a tuple with exactly the number of items specified by the format string, or a single mapping object (for example, a dictionary).

.. index:: single: () (parentheses); in printf-style formatting single: * (asterisk); in printf-style formatting single: . (dot); in printf-style formatting

A conversion specifier contains two or more characters and has the following components, which must occur in this order:

#. The '%' character, which marks the start of the specifier.

#. Mapping key (optional), consisting of a parenthesised sequence of characters (for example, (somename)).

#. Conversion flags (optional), which affect the result of some conversion types.

#. Minimum field width (optional). If specified as an '*' (asterisk), the actual width is read from the next element of the tuple in values, and the object to convert comes after the minimum field width and optional precision.

#. Precision (optional), given as a '.' (dot) followed by the precision. If specified as '*' (an asterisk), the actual precision is read from the next element of the tuple in values, and the value to convert comes after the precision.

#. Length modifier (optional).

#. Conversion type.

When the right argument is a dictionary (or other mapping type), then the formats in the string must include a parenthesised mapping key into that dictionary inserted immediately after the '%' character. The mapping key selects the value to be formatted from the mapping. For example:

print('%(language)s has %(number)03d quote types.' % ... {'language': "Python", "number": 2}) Python has 002 quote types.

In this case no * specifiers may occur in a format (since they require a sequential parameter list).

The conversion flag characters are:

.. index:: single: # (hash); in printf-style formatting single: - (minus); in printf-style formatting single: + (plus); in printf-style formatting single: space; in printf-style formatting

+---------+---------------------------------------------------------------------+ | Flag | Meaning | +=========+=====================================================================+ | '#' | The value conversion will use the "alternate form" (where defined | | | below). | +---------+---------------------------------------------------------------------+ | '0' | The conversion will be zero padded for numeric values. | +---------+---------------------------------------------------------------------+ | '-' | The converted value is left adjusted (overrides the '0' | | | conversion if both are given). | +---------+---------------------------------------------------------------------+ | ' ' | (a space) A blank should be left before a positive number (or empty | | | string) produced by a signed conversion. | +---------+---------------------------------------------------------------------+ | '+' | A sign character ('+' or '-') will precede the conversion | | | (overrides a "space" flag). | +---------+---------------------------------------------------------------------+

A length modifier (h, l, or L) may be present, but is ignored as it is not necessary for Python -- so e.g. %ld is identical to %d.

The conversion types are:

+------------+-----------------------------------------------------+-------+ | Conversion | Meaning | Notes | +============+=====================================================+=======+ | 'd' | Signed integer decimal. | | +------------+-----------------------------------------------------+-------+ | 'i' | Signed integer decimal. | | +------------+-----------------------------------------------------+-------+ | 'o' | Signed octal value. | (1) | +------------+-----------------------------------------------------+-------+ | 'u' | Obsolete type -- it is identical to 'd'. | (6) | +------------+-----------------------------------------------------+-------+ | 'x' | Signed hexadecimal (lowercase). | (2) | +------------+-----------------------------------------------------+-------+ | 'X' | Signed hexadecimal (uppercase). | (2) | +------------+-----------------------------------------------------+-------+ | 'e' | Floating-point exponential format (lowercase). | (3) | +------------+-----------------------------------------------------+-------+ | 'E' | Floating-point exponential format (uppercase). | (3) | +------------+-----------------------------------------------------+-------+ | 'f' | Floating-point decimal format. | (3) | +------------+-----------------------------------------------------+-------+ | 'F' | Floating-point decimal format. | (3) | +------------+-----------------------------------------------------+-------+ | 'g' | Floating-point format. Uses lowercase exponential | (4) | | | format if exponent is less than -4 or not less than | | | | precision, decimal format otherwise. | | +------------+-----------------------------------------------------+-------+ | 'G' | Floating-point format. Uses uppercase exponential | (4) | | | format if exponent is less than -4 or not less than | | | | precision, decimal format otherwise. | | +------------+-----------------------------------------------------+-------+ | 'c' | Single character (accepts integer or single | | | | character string). | | +------------+-----------------------------------------------------+-------+ | 'r' | String (converts any Python object using | (5) | | | :func:repr). | | +------------+-----------------------------------------------------+-------+ | 's' | String (converts any Python object using | (5) | | | :func:str). | | +------------+-----------------------------------------------------+-------+ | 'a' | String (converts any Python object using | (5) | | | :func:ascii). | | +------------+-----------------------------------------------------+-------+ | '%' | No argument is converted, results in a '%' | | | | character in the result. | | +------------+-----------------------------------------------------+-------+

For floating-point formats, the result should be correctly rounded to a given precision p of digits after the decimal point. The rounding mode matches that of the :func:round builtin.

Notes:

(1) The alternate form causes a leading octal specifier ('0o') to be inserted before the first digit.

(2) The alternate form causes a leading '0x' or '0X' (depending on whether the 'x' or 'X' format was used) to be inserted before the first digit.

(3) The alternate form causes the result to always contain a decimal point, even if no digits follow it.

The precision determines the number of digits after the decimal point and defaults to 6.

(4) The alternate form causes the result to always contain a decimal point, and trailing zeroes are not removed as they would otherwise be.

The precision determines the number of significant digits before and after the decimal point and defaults to 6.

(5) If precision is N, the output is truncated to N characters.

(6) See :pep:237.

Since Python strings have an explicit length, %s conversions do not assume that '\0' is the end of the string.

.. XXX Examples?

.. versionchanged:: 3.1 %f conversions for numbers whose absolute value is over 1e50 are no longer replaced by %g conversions.

.. index:: single: buffer protocol; binary sequence types

.. _binaryseq:

Binary Sequence Types --- :class:`bytes`, :class:`bytearray`, :class:`memoryview`

.. index:: pair: object; bytes pair: object; bytearray pair: object; memoryview pair: module; array

The core built-in types for manipulating binary data are :class:bytes and :class:bytearray. They are supported by :class:memoryview which uses the :ref:buffer protocol <bufferobjects> to access the memory of other binary objects without needing to make a copy.

The :mod:array module supports efficient storage of basic data types like 32-bit integers and IEEE754 double-precision floating values.

.. _typebytes:

Bytes Objects

.. index:: pair: object; bytes

Bytes objects are immutable sequences of single bytes. Since many major binary protocols are based on the ASCII text encoding, bytes objects offer several methods that are only valid when working with ASCII compatible data and are closely related to string objects in a variety of other ways.

.. class:: bytes(source=b'') bytes(source, encoding, errors='strict')

Firstly, the syntax for bytes literals is largely the same as that for string literals, except that a b prefix is added:

Single quotes: b'still allows embedded "double" quotes'
Double quotes: b"still allows embedded 'single' quotes"
Triple quoted: b'''3 single quotes''', b"""3 double quotes"""

Only ASCII characters are permitted in bytes literals (regardless of the declared source code encoding). Any binary values over 127 must be entered into bytes literals using the appropriate escape sequence.

As with string literals, bytes literals may also use a r prefix to disable processing of escape sequences. See :ref:strings for more about the various forms of bytes literal, including supported escape sequences.

While bytes literals and representations are based on ASCII text, bytes objects actually behave like immutable sequences of integers, with each value in the sequence restricted such that 0 <= x < 256 (attempts to violate this restriction will trigger :exc:ValueError). This is done deliberately to emphasise that while many binary formats include ASCII based elements and can be usefully manipulated with some text-oriented algorithms, this is not generally the case for arbitrary binary data (blindly applying text processing algorithms to binary data formats that are not ASCII compatible will usually lead to data corruption).

In addition to the literal forms, bytes objects can be created in a number of other ways:

A zero-filled bytes object of a specified length: bytes(10)
From an iterable of integers: bytes(range(20))
Copying existing binary data via the buffer protocol: bytes(obj)

Also see the :ref:bytes <func-bytes> built-in.

Since 2 hexadecimal digits correspond precisely to a single byte, hexadecimal numbers are a commonly used format for describing binary data. Accordingly, the bytes type has an additional class method to read data in that format:

.. classmethod:: fromhex(string, /)

  This :class:`bytes` class method returns a bytes object, decoding the
  given string object.  The string must contain two hexadecimal digits per
  byte, with ASCII whitespace being ignored.

  >>> bytes.fromhex('2Ef0 F1f2  ')
  b'.\xf0\xf1\xf2'

  .. versionchanged:: 3.7
     :meth:`bytes.fromhex` now skips all ASCII whitespace in the string,
     not just spaces.

  .. versionchanged:: 3.14
     :meth:`bytes.fromhex` now accepts ASCII :class:`bytes` and
     :term:`bytes-like objects <bytes-like object>` as input.

A reverse conversion function exists to transform a bytes object into its hexadecimal representation.

.. method:: hex(*, bytes_per_sep=1) hex(sep, bytes_per_sep=1)

  Return a string object containing two hexadecimal digits for each
  byte in the instance.

  >>> b'\xf0\xf1\xf2'.hex()
  'f0f1f2'

  If you want to make the hex string easier to read, you can specify a
  single character separator *sep* parameter to include in the output.
  By default, this separator will be included between each byte.
  A second optional *bytes_per_sep* parameter controls the spacing.
  Positive values calculate the separator position from the right,
  negative values from the left.

  >>> value = b'\xf0\xf1\xf2'
  >>> value.hex('-')
  'f0-f1-f2'
  >>> value.hex('_', 2)
  'f0_f1f2'
  >>> b'UUDDLRLRAB'.hex(' ', -4)
  '55554444 4c524c52 4142'

  .. versionadded:: 3.5

  .. versionchanged:: 3.8
     :meth:`bytes.hex` now supports optional *sep* and *bytes_per_sep*
     parameters to insert separators between bytes in the hex output.

Since bytes objects are sequences of integers (akin to a tuple), for a bytes object b, b[0] will be an integer, while b[0:1] will be a bytes object of length 1. (This contrasts with text strings, where both indexing and slicing will produce a string of length 1)

The representation of bytes objects uses the literal format (b'...') since it is often more useful than e.g. bytes([46, 46, 46]). You can always convert a bytes object into a list of integers using list(b).

.. _typebytearray:

Bytearray Objects

.. index:: pair: object; bytearray

:class:bytearray objects are a mutable counterpart to :class:bytes objects.

.. class:: bytearray(source=b'') bytearray(source, encoding, errors='strict')

There is no dedicated literal syntax for bytearray objects, instead they are always created by calling the constructor:

Creating an empty instance: bytearray()
Creating a zero-filled instance with a given length: bytearray(10)
From an iterable of integers: bytearray(range(20))
Copying existing binary data via the buffer protocol: bytearray(b'Hi!')

As bytearray objects are mutable, they support the :ref:mutable <typesseq-mutable> sequence operations in addition to the common bytes and bytearray operations described in :ref:bytes-methods.

Also see the :ref:bytearray <func-bytearray> built-in.

Since 2 hexadecimal digits correspond precisely to a single byte, hexadecimal numbers are a commonly used format for describing binary data. Accordingly, the bytearray type has an additional class method to read data in that format:

.. classmethod:: fromhex(string, /)

  This :class:`bytearray` class method returns bytearray object, decoding
  the given string object.  The string must contain two hexadecimal digits
  per byte, with ASCII whitespace being ignored.

  >>> bytearray.fromhex('2Ef0 F1f2  ')
  bytearray(b'.\xf0\xf1\xf2')

  .. versionchanged:: 3.7
     :meth:`bytearray.fromhex` now skips all ASCII whitespace in the string,
     not just spaces.

  .. versionchanged:: 3.14
     :meth:`bytearray.fromhex` now accepts ASCII :class:`bytes` and
     :term:`bytes-like objects <bytes-like object>` as input.

A reverse conversion function exists to transform a bytearray object into its hexadecimal representation.

.. method:: hex(*, bytes_per_sep=1) hex(sep, bytes_per_sep=1)

  Return a string object containing two hexadecimal digits for each
  byte in the instance.

  >>> bytearray(b'\xf0\xf1\xf2').hex()
  'f0f1f2'

  .. versionadded:: 3.5

  .. versionchanged:: 3.8
     Similar to :meth:`bytes.hex`, :meth:`bytearray.hex` now supports
     optional *sep* and *bytes_per_sep* parameters to insert separators
     between bytes in the hex output.

.. method:: resize(size, /)

  Resize the :class:`bytearray` to contain *size* bytes. *size* must be
  greater than or equal to 0.

  If the :class:`bytearray` needs to shrink, bytes beyond *size* are truncated.

  If the :class:`bytearray` needs to grow, all new bytes, those beyond *size*,
  will be set to null bytes.


  This is equivalent to:

  >>> def resize(ba, size):
  ...     if len(ba) > size:
  ...         del ba[size:]
  ...     else:
  ...         ba += b'\0' * (size - len(ba))

  Examples:

  >>> shrink = bytearray(b'abc')
  >>> shrink.resize(1)
  >>> (shrink, len(shrink))
  (bytearray(b'a'), 1)
  >>> grow = bytearray(b'abc')
  >>> grow.resize(5)
  >>> (grow, len(grow))
  (bytearray(b'abc\x00\x00'), 5)

  .. versionadded:: 3.14

.. method:: take_bytes(n=None, /)

  Remove the first *n* bytes from the bytearray and return them as an immutable
  :class:`bytes`.
  By default (if *n* is ``None``), return all bytes and clear the bytearray.

  If *n* is negative, index from the end and take the first :func:`len`
  plus *n* bytes. If *n* is out of bounds, raise :exc:`IndexError`.

  Taking less than the full length will leave remaining bytes in the
  :class:`bytearray`, which requires a copy. If the remaining bytes should be
  discarded, use :func:`~bytearray.resize` or :keyword:`del` to truncate
  then :func:`~bytearray.take_bytes` without a size.

  .. impl-detail::

     Taking all bytes is a zero-copy operation.

  .. versionadded:: 3.15

     See the :ref:`What's New <whatsnew315-bytearray-take-bytes>` entry for
     common code patterns which can be optimized with
     :meth:`bytearray.take_bytes`.

Since bytearray objects are sequences of integers (akin to a list), for a bytearray object b, b[0] will be an integer, while b[0:1] will be a bytearray object of length 1. (This contrasts with text strings, where both indexing and slicing will produce a string of length 1)

The representation of bytearray objects uses the bytes literal format (bytearray(b'...')) since it is often more useful than e.g. bytearray([46, 46, 46]). You can always convert a bytearray object into a list of integers using list(b).

.. seealso::

For detailed information on thread-safety guarantees for :class:bytearray objects, see :ref:thread-safety-bytearray.

.. _bytes-methods:

Bytes and Bytearray Operations

.. index:: pair: bytes; methods pair: bytearray; methods

Both bytes and bytearray objects support the :ref:common <typesseq-common> sequence operations. They interoperate not just with operands of the same type, but with any :term:bytes-like object. Due to this flexibility, they can be freely mixed in operations without causing errors. However, the return type of the result may depend on the order of operands.

.. note::

The methods on bytes and bytearray objects don't accept strings as their arguments, just as the methods on strings don't accept bytes as their arguments. For example, you have to write::

  a = "abc"
  b = a.replace("a", "f")

and::

  a = b"abc"
  b = a.replace(b"a", b"f")

Some bytes and bytearray operations assume the use of ASCII compatible binary formats, and hence should be avoided when working with arbitrary binary data. These restrictions are covered below.

.. note:: Using these ASCII based operations to manipulate binary data that is not stored in an ASCII based format may lead to data corruption.

The following methods on bytes and bytearray objects can be used with arbitrary binary data.

.. method:: bytes.count(sub[, start[, end]]) bytearray.count(sub[, start[, end]])

Return the number of non-overlapping occurrences of subsequence sub in the range [start, end]. Optional arguments start and end are interpreted as in slice notation.

The subsequence to search for may be any :term:bytes-like object or an integer in the range 0 to 255.

If sub is empty, returns the number of empty slices between characters which is the length of the bytes object plus one.

.. versionchanged:: 3.3 Also accept an integer in the range 0 to 255 as the subsequence.

.. method:: bytes.removeprefix(prefix, /) bytearray.removeprefix(prefix, /)

If the binary data starts with the prefix string, return bytes[len(prefix):]. Otherwise, return a copy of the original binary data::

  >>> b'TestHook'.removeprefix(b'Test')
  b'Hook'
  >>> b'BaseTestCase'.removeprefix(b'Test')
  b'BaseTestCase'

The prefix may be any :term:bytes-like object.

.. note::

  The bytearray version of this method does *not* operate in place -
  it always produces a new object, even if no changes were made.

.. versionadded:: 3.9

.. method:: bytes.removesuffix(suffix, /) bytearray.removesuffix(suffix, /)

If the binary data ends with the suffix string and that suffix is not empty, return bytes[:-len(suffix)]. Otherwise, return a copy of the original binary data::

  >>> b'MiscTests'.removesuffix(b'Tests')
  b'Misc'
  >>> b'TmpDirMixin'.removesuffix(b'Tests')
  b'TmpDirMixin'

The suffix may be any :term:bytes-like object.

.. note::

  The bytearray version of this method does *not* operate in place -
  it always produces a new object, even if no changes were made.

.. versionadded:: 3.9

.. method:: bytes.decode(encoding="utf-8", errors="strict") bytearray.decode(encoding="utf-8", errors="strict")

Return the bytes decoded to a :class:str.

encoding defaults to 'utf-8'; see :ref:standard-encodings for possible values.

errors controls how decoding errors are handled. If 'strict' (the default), a :exc:UnicodeError exception is raised. Other possible values are 'ignore', 'replace', and any other name registered via :func:codecs.register_error. See :ref:error-handlers for details.

For performance reasons, the value of errors is not checked for validity unless a decoding error actually occurs, :ref:devmode is enabled or a :ref:debug build <debug-build> is used.

.. note::

  Passing the *encoding* argument to :class:`str` allows decoding any
  :term:`bytes-like object` directly, without needing to make a temporary
  :class:`!bytes` or :class:`!bytearray` object.

.. versionchanged:: 3.1 Added support for keyword arguments.

.. versionchanged:: 3.9 The value of the errors argument is now checked in :ref:devmode and in :ref:debug mode <debug-build>.

.. method:: bytes.endswith(suffix[, start[, end]]) bytearray.endswith(suffix[, start[, end]])

Return True if the binary data ends with the specified suffix, otherwise return False. suffix can also be a tuple of suffixes to look for. With optional start, test beginning at that position. With optional end, stop comparing at that position.

The suffix(es) to search for may be any :term:bytes-like object.

.. method:: bytes.find(sub[, start[, end]]) bytearray.find(sub[, start[, end]])

Return the lowest index in the data where the subsequence sub is found, such that sub is contained in the slice s[start:end]. Optional arguments start and end are interpreted as in slice notation. Return -1 if sub is not found.

The subsequence to search for may be any :term:bytes-like object or an integer in the range 0 to 255.

.. note::

  The :meth:`~bytes.find` method should be used only if you need to know the
  position of *sub*.  To check if *sub* is a substring or not, use the
  :keyword:`in` operator::

     >>> b'Py' in b'Python'
     True

.. versionchanged:: 3.3 Also accept an integer in the range 0 to 255 as the subsequence.

.. method:: bytes.index(sub[, start[, end]]) bytearray.index(sub[, start[, end]])

Like :meth:~bytes.find, but raise :exc:ValueError when the subsequence is not found.

The subsequence to search for may be any :term:bytes-like object or an integer in the range 0 to 255.

.. versionchanged:: 3.3 Also accept an integer in the range 0 to 255 as the subsequence.

.. method:: bytes.join(iterable, /) bytearray.join(iterable, /)

Return a bytes or bytearray object which is the concatenation of the binary data sequences in iterable. A :exc:TypeError will be raised if there are any values in iterable that are not :term:bytes-like objects <bytes-like object>, including :class:str objects. The separator between elements is the contents of the bytes or bytearray object providing this method.

.. staticmethod:: bytes.maketrans(from, to, /) bytearray.maketrans(from, to, /)

This static method returns a translation table usable for :meth:bytes.translate that will map each character in from into the character at the same position in to; from and to must both be :term:bytes-like objects <bytes-like object> and have the same length.

.. versionadded:: 3.1

.. method:: bytes.partition(sep, /) bytearray.partition(sep, /)

Split the sequence at the first occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself or its bytearray copy, and the part after the separator. If the separator is not found, return a 3-tuple containing a copy of the original sequence, followed by two empty bytes or bytearray objects.

The separator to search for may be any :term:bytes-like object.

.. method:: bytes.replace(old, new, /, count=-1) bytearray.replace(old, new, /, count=-1)

Return a copy of the sequence with all occurrences of subsequence old replaced by new. If count is given, only the first count occurrences are replaced. If count is not specified or -1, then all occurrences are replaced.

The subsequence to search for and its replacement may be any :term:bytes-like object.

.. note::

  The bytearray version of this method does *not* operate in place - it
  always produces a new object, even if no changes were made.

.. versionchanged:: 3.15 count is now supported as a keyword argument.

.. method:: bytes.rfind(sub[, start[, end]]) bytearray.rfind(sub[, start[, end]])

Return the highest index in the sequence where the subsequence sub is found, such that sub is contained within s[start:end]. Optional arguments start and end are interpreted as in slice notation. Return -1 on failure.

The subsequence to search for may be any :term:bytes-like object or an integer in the range 0 to 255.

.. versionchanged:: 3.3 Also accept an integer in the range 0 to 255 as the subsequence.

.. method:: bytes.rindex(sub[, start[, end]]) bytearray.rindex(sub[, start[, end]])

Like :meth:~bytes.rfind but raises :exc:ValueError when the subsequence sub is not found.

The subsequence to search for may be any :term:bytes-like object or an integer in the range 0 to 255.

.. versionchanged:: 3.3 Also accept an integer in the range 0 to 255 as the subsequence.

.. method:: bytes.rpartition(sep, /) bytearray.rpartition(sep, /)

Split the sequence at the last occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself or its bytearray copy, and the part after the separator. If the separator is not found, return a 3-tuple containing two empty bytes or bytearray objects, followed by a copy of the original sequence.

The separator to search for may be any :term:bytes-like object.

.. method:: bytes.startswith(prefix[, start[, end]]) bytearray.startswith(prefix[, start[, end]])

Return True if the binary data starts with the specified prefix, otherwise return False. prefix can also be a tuple of prefixes to look for. With optional start, test beginning at that position. With optional end, stop comparing at that position.

The prefix(es) to search for may be any :term:bytes-like object.

.. method:: bytes.translate(table, /, delete=b'') bytearray.translate(table, /, delete=b'')

Return a copy of the bytes or bytearray object where all bytes occurring in the optional argument delete are removed, and the remaining bytes have been mapped through the given translation table, which must be a bytes object of length 256.

You can use the :func:bytes.maketrans method to create a translation table.

Set the table argument to None for translations that only delete characters::

  >>> b'read this short text'.translate(None, b'aeiou')
  b'rd ths shrt txt'

.. versionchanged:: 3.6 delete is now supported as a keyword argument.

The following methods on bytes and bytearray objects have default behaviours that assume the use of ASCII compatible binary formats, but can still be used with arbitrary binary data by passing appropriate arguments. Note that all of the bytearray methods in this section do not operate in place, and instead produce new objects.

.. method:: bytes.center(width, fillbyte=b' ', /) bytearray.center(width, fillbyte=b' ', /)

Return a copy of the object centered in a sequence of length width. Padding is done using the specified fillbyte (default is an ASCII space). For :class:bytes objects, the original sequence is returned if width is less than or equal to len(s).

.. note::

  The bytearray version of this method does *not* operate in place -
  it always produces a new object, even if no changes were made.

.. method:: bytes.ljust(width, fillbyte=b' ', /) bytearray.ljust(width, fillbyte=b' ', /)

Return a copy of the object left justified in a sequence of length width. Padding is done using the specified fillbyte (default is an ASCII space). For :class:bytes objects, the original sequence is returned if width is less than or equal to len(s).

.. note::

  The bytearray version of this method does *not* operate in place -
  it always produces a new object, even if no changes were made.

.. method:: bytes.lstrip(bytes=None, /) bytearray.lstrip(bytes=None, /)

Return a copy of the sequence with specified leading bytes removed. The bytes argument is a binary sequence specifying the set of byte values to be removed. If omitted or None, the bytes argument defaults to removing ASCII whitespace. The bytes argument is not a prefix; rather, all combinations of its values are stripped::

  >>> b'   spacious   '.lstrip()
  b'spacious   '
  >>> b'www.example.com'.lstrip(b'cmowz.')
  b'example.com'

The binary sequence of byte values to remove may be any :term:bytes-like object. See :meth:~bytes.removeprefix for a method that will remove a single prefix string rather than all of a set of characters. For example::

  >>> b'Arthur: three!'.lstrip(b'Arthur: ')
  b'ee!'
  >>> b'Arthur: three!'.removeprefix(b'Arthur: ')
  b'three!'

.. note::

  The bytearray version of this method does *not* operate in place -
  it always produces a new object, even if no changes were made.

.. method:: bytes.rjust(width, fillbyte=b' ', /) bytearray.rjust(width, fillbyte=b' ', /)

Return a copy of the object right justified in a sequence of length width. Padding is done using the specified fillbyte (default is an ASCII space). For :class:bytes objects, the original sequence is returned if width is less than or equal to len(s).

.. note::

  The bytearray version of this method does *not* operate in place -
  it always produces a new object, even if no changes were made.

.. method:: bytes.rsplit(sep=None, maxsplit=-1) bytearray.rsplit(sep=None, maxsplit=-1)

Split the binary sequence into subsequences of the same type, using sep as the delimiter string. If maxsplit is given, at most maxsplit splits are done, the rightmost ones. If sep is not specified or None, any subsequence consisting solely of ASCII whitespace is a separator. Except for splitting from the right, :meth:rsplit behaves like :meth:split which is described in detail below.

.. method:: bytes.rstrip(bytes=None, /) bytearray.rstrip(bytes=None, /)

Return a copy of the sequence with specified trailing bytes removed. The bytes argument is a binary sequence specifying the set of byte values to be removed. If omitted or None, the bytes argument defaults to removing ASCII whitespace. The bytes argument is not a suffix; rather, all combinations of its values are stripped::

  >>> b'   spacious   '.rstrip()
  b'   spacious'
  >>> b'mississippi'.rstrip(b'ipz')
  b'mississ'

The binary sequence of byte values to remove may be any :term:bytes-like object. See :meth:~bytes.removesuffix for a method that will remove a single suffix string rather than all of a set of characters. For example::

  >>> b'Monty Python'.rstrip(b' Python')
  b'M'
  >>> b'Monty Python'.removesuffix(b' Python')
  b'Monty'

.. note::

  The bytearray version of this method does *not* operate in place -
  it always produces a new object, even if no changes were made.

.. method:: bytes.split(sep=None, maxsplit=-1) bytearray.split(sep=None, maxsplit=-1)

Split the binary sequence into subsequences of the same type, using sep as the delimiter string. If maxsplit is given and non-negative, at most maxsplit splits are done (thus, the list will have at most maxsplit+1 elements). If maxsplit is not specified or is -1, then there is no limit on the number of splits (all possible splits are made).

If sep is given, consecutive delimiters are not grouped together and are deemed to delimit empty subsequences (for example, b'1,,2'.split(b',') returns [b'1', b'', b'2']). The sep argument may consist of a multibyte sequence as a single delimiter. Splitting an empty sequence with a specified separator returns [b''] or [bytearray(b'')] depending on the type of object being split. The sep argument may be any :term:bytes-like object.

For example::

  >>> b'1,2,3'.split(b',')
  [b'1', b'2', b'3']
  >>> b'1,2,3'.split(b',', maxsplit=1)
  [b'1', b'2,3']
  >>> b'1,2,,3,'.split(b',')
  [b'1', b'2', b'', b'3', b'']
  >>> b'1<>2<>3<4'.split(b'<>')
  [b'1', b'2', b'3<4']

If sep is not specified or is None, a different splitting algorithm is applied: runs of consecutive ASCII whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the sequence has leading or trailing whitespace. Consequently, splitting an empty sequence or a sequence consisting solely of ASCII whitespace without a specified separator returns [].

For example::

  >>> b'1 2 3'.split()
  [b'1', b'2', b'3']
  >>> b'1 2 3'.split(maxsplit=1)
  [b'1', b'2 3']
  >>> b'   1   2   3   '.split()
  [b'1', b'2', b'3']

.. method:: bytes.strip(bytes=None, /) bytearray.strip(bytes=None, /)

Return a copy of the sequence with specified leading and trailing bytes removed. The bytes argument is a binary sequence specifying the set of byte values to be removed. If omitted or None, the bytes argument defaults to removing ASCII whitespace. The bytes argument is not a prefix or suffix; rather, all combinations of its values are stripped::

  >>> b'   spacious   '.strip()
  b'spacious'
  >>> b'www.example.com'.strip(b'cmowz.')
  b'example'

The binary sequence of byte values to remove may be any :term:bytes-like object.

.. note::

  The bytearray version of this method does *not* operate in place -
  it always produces a new object, even if no changes were made.

The following methods on bytes and bytearray objects assume the use of ASCII compatible binary formats and should not be applied to arbitrary binary data. Note that all of the bytearray methods in this section do not operate in place, and instead produce new objects.

.. method:: bytes.capitalize() bytearray.capitalize()

Return a copy of the sequence with each byte interpreted as an ASCII character, and the first byte capitalized and the rest lowercased. Non-ASCII byte values are passed through unchanged.

.. note::

  The bytearray version of this method does *not* operate in place - it
  always produces a new object, even if no changes were made.

.. method:: bytes.expandtabs(tabsize=8) bytearray.expandtabs(tabsize=8)

Return a copy of the sequence where all ASCII tab characters are replaced by one or more ASCII spaces, depending on the current column and the given tab size. Tab positions occur every tabsize bytes (default is 8, giving tab positions at columns 0, 8, 16 and so on). To expand the sequence, the current column is set to zero and the sequence is examined byte by byte. If the byte is an ASCII tab character (b'\t'), one or more space characters are inserted in the result until the current column is equal to the next tab position. (The tab character itself is not copied.) If the current byte is an ASCII newline (b'\n') or carriage return (b'\r'), it is copied and the current column is reset to zero. Any other byte value is copied unchanged and the current column is incremented by one regardless of how the byte value is represented when printed::

  >>> b'01\t012\t0123\t01234'.expandtabs()
  b'01      012     0123    01234'
  >>> b'01\t012\t0123\t01234'.expandtabs(4)
  b'01  012 0123    01234'

.. note::

  The bytearray version of this method does *not* operate in place - it
  always produces a new object, even if no changes were made.

.. method:: bytes.isalnum() bytearray.isalnum()

Return True if all bytes in the sequence are alphabetical ASCII characters or ASCII decimal digits and the sequence is not empty, False otherwise. Alphabetic ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'. ASCII decimal digits are those byte values in the sequence b'0123456789'.

For example::

  >>> b'ABCabc1'.isalnum()
  True
  >>> b'ABC abc1'.isalnum()
  False

.. method:: bytes.isalpha() bytearray.isalpha()

Return True if all bytes in the sequence are alphabetic ASCII characters and the sequence is not empty, False otherwise. Alphabetic ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'.

For example::

  >>> b'ABCabc'.isalpha()
  True
  >>> b'ABCabc1'.isalpha()
  False

.. method:: bytes.isascii() bytearray.isascii()

Return True if the sequence is empty or all bytes in the sequence are ASCII, False otherwise. ASCII bytes are in the range 0-0x7F.

.. versionadded:: 3.7

.. method:: bytes.isdigit() bytearray.isdigit()

Return True if all bytes in the sequence are ASCII decimal digits and the sequence is not empty, False otherwise. ASCII decimal digits are those byte values in the sequence b'0123456789'.

For example::

  >>> b'1234'.isdigit()
  True
  >>> b'1.23'.isdigit()
  False

.. method:: bytes.islower() bytearray.islower()

Return True if there is at least one lowercase ASCII character in the sequence and no uppercase ASCII characters, False otherwise.

For example::

  >>> b'hello world'.islower()
  True
  >>> b'Hello world'.islower()
  False

Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz'. Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.

.. method:: bytes.isspace() bytearray.isspace()

Return True if all bytes in the sequence are ASCII whitespace and the sequence is not empty, False otherwise. ASCII whitespace characters are those byte values in the sequence b' \t\n\r\x0b\f' (space, tab, newline, carriage return, vertical tab, form feed).

.. method:: bytes.istitle() bytearray.istitle()

Return True if the sequence is ASCII titlecase and the sequence is not empty, False otherwise. See :meth:bytes.title for more details on the definition of "titlecase".

For example::

  >>> b'Hello World'.istitle()
  True
  >>> b'Hello world'.istitle()
  False

.. method:: bytes.isupper() bytearray.isupper()

Return True if there is at least one uppercase alphabetic ASCII character in the sequence and no lowercase ASCII characters, False otherwise.

For example::

  >>> b'HELLO WORLD'.isupper()
  True
  >>> b'Hello world'.isupper()
  False

Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz'. Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.

.. method:: bytes.lower() bytearray.lower()

Return a copy of the sequence with all the uppercase ASCII characters converted to their corresponding lowercase counterpart.

For example::

  >>> b'Hello World'.lower()
  b'hello world'

Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz'. Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.

.. note::

  The bytearray version of this method does *not* operate in place - it
  always produces a new object, even if no changes were made.

.. index:: single: universal newlines; bytes.splitlines method single: universal newlines; bytearray.splitlines method

.. method:: bytes.splitlines(keepends=False) bytearray.splitlines(keepends=False)

Return a list of the lines in the binary sequence, breaking at ASCII line boundaries. This method uses the :term:universal newlines approach to splitting lines. Line breaks are not included in the resulting list unless keepends is given and true.

For example::

  >>> b'ab c\n\nde fg\rkl\r\n'.splitlines()
  [b'ab c', b'', b'de fg', b'kl']
  >>> b'ab c\n\nde fg\rkl\r\n'.splitlines(keepends=True)
  [b'ab c\n', b'\n', b'de fg\r', b'kl\r\n']

Unlike :meth:~bytes.split when a delimiter string sep is given, this method returns an empty list for the empty string, and a terminal line break does not result in an extra line::

  >>> b"".split(b'\n'), b"Two lines\n".split(b'\n')
  ([b''], [b'Two lines', b''])
  >>> b"".splitlines(), b"One line\n".splitlines()
  ([], [b'One line'])

.. method:: bytes.swapcase() bytearray.swapcase()

Return a copy of the sequence with all the lowercase ASCII characters converted to their corresponding uppercase counterpart and vice-versa.

For example::

  >>> b'Hello World'.swapcase()
  b'hELLO wORLD'

Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz'. Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.

Unlike :func:str.swapcase, it is always the case that bin.swapcase().swapcase() == bin for the binary versions. Case conversions are symmetrical in ASCII, even though that is not generally true for arbitrary Unicode code points.

.. note::

  The bytearray version of this method does *not* operate in place - it
  always produces a new object, even if no changes were made.

.. method:: bytes.title() bytearray.title()

Return a titlecased version of the binary sequence where words start with an uppercase ASCII character and the remaining characters are lowercase. Uncased byte values are left unmodified.

For example::

  >>> b'Hello world'.title()
  b'Hello World'

Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz'. Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'. All other byte values are uncased.

    >>> b"they're bill's friends from the UK".title()
    b"They'Re Bill'S Friends From The Uk"

A workaround for apostrophes can be constructed using regular expressions::

    >>> import re
    >>> def titlecase(s):
    ...     return re.sub(rb"[A-Za-z]+('[A-Za-z]+)?",
    ...                   lambda mo: mo.group(0)[0:1].upper() +
    ...                              mo.group(0)[1:].lower(),
    ...                   s)
    ...
    >>> titlecase(b"they're bill's friends.")
    b"They're Bill's Friends."

.. note::

  The bytearray version of this method does *not* operate in place - it
  always produces a new object, even if no changes were made.

.. method:: bytes.upper() bytearray.upper()

Return a copy of the sequence with all the lowercase ASCII characters converted to their corresponding uppercase counterpart.

For example::

  >>> b'Hello World'.upper()
  b'HELLO WORLD'

Lowercase ASCII characters are those byte values in the sequence b'abcdefghijklmnopqrstuvwxyz'. Uppercase ASCII characters are those byte values in the sequence b'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.

.. note::

  The bytearray version of this method does *not* operate in place - it
  always produces a new object, even if no changes were made.

.. method:: bytes.zfill(width, /) bytearray.zfill(width, /)

Return a copy of the sequence left filled with ASCII b'0' digits to make a sequence of length width. A leading sign prefix (b'+'/ b'-') is handled by inserting the padding after the sign character rather than before. For :class:bytes objects, the original sequence is returned if width is less than or equal to len(seq).

For example::

  >>> b"42".zfill(5)
  b'00042'
  >>> b"-42".zfill(5)
  b'-0042'

.. note::

  The bytearray version of this method does *not* operate in place - it
  always produces a new object, even if no changes were made.

.. _bytes-formatting:

`printf`-style Bytes Formatting

.. index:: single: formatting; bytes (%) single: formatting; bytearray (%) single: interpolation; bytes (%) single: interpolation; bytearray (%) single: bytes; formatting single: bytearray; formatting single: bytes; interpolation single: bytearray; interpolation single: printf-style formatting single: sprintf-style formatting single: % (percent); printf-style formatting

.. note::

The formatting operations described here exhibit a variety of quirks that lead to a number of common errors (such as failing to display tuples and dictionaries correctly). If the value being printed may be a tuple or dictionary, wrap it in a tuple.

Bytes objects (bytes/bytearray) have one unique built-in operation: the % operator (modulo). This is also known as the bytes formatting or interpolation operator. Given format % values (where format is a bytes object), % conversion specifications in format are replaced with zero or more elements of values. The effect is similar to using the :c:func:sprintf in the C language.

If format requires a single argument, values may be a single non-tuple object. [5]_ Otherwise, values must be a tuple with exactly the number of items specified by the format bytes object, or a single mapping object (for example, a dictionary).

.. index:: single: () (parentheses); in printf-style formatting single: * (asterisk); in printf-style formatting single: . (dot); in printf-style formatting

A conversion specifier contains two or more characters and has the following components, which must occur in this order:

#. The '%' character, which marks the start of the specifier.

#. Mapping key (optional), consisting of a parenthesised sequence of characters (for example, (somename)).

#. Conversion flags (optional), which affect the result of some conversion types.

#. Length modifier (optional).

#. Conversion type.

When the right argument is a dictionary (or other mapping type), then the formats in the bytes object must include a parenthesised mapping key into that dictionary inserted immediately after the '%' character. The mapping key selects the value to be formatted from the mapping. For example:

print(b'%(language)s has %(number)03d quote types.' % ... {b'language': b"Python", b"number": 2}) b'Python has 002 quote types.'

In this case no * specifiers may occur in a format (since they require a sequential parameter list).

The conversion flag characters are:

.. index:: single: # (hash); in printf-style formatting single: - (minus); in printf-style formatting single: + (plus); in printf-style formatting single: space; in printf-style formatting

A length modifier (h, l, or L) may be present, but is ignored as it is not necessary for Python -- so e.g. %ld is identical to %d.

The conversion types are:

+------------+-----------------------------------------------------+-------+ | Conversion | Meaning | Notes | +============+=====================================================+=======+ | 'd' | Signed integer decimal. | | +------------+-----------------------------------------------------+-------+ | 'i' | Signed integer decimal. | | +------------+-----------------------------------------------------+-------+ | 'o' | Signed octal value. | (1) | +------------+-----------------------------------------------------+-------+ | 'u' | Obsolete type -- it is identical to 'd'. | (8) | +------------+-----------------------------------------------------+-------+ | 'x' | Signed hexadecimal (lowercase). | (2) | +------------+-----------------------------------------------------+-------+ | 'X' | Signed hexadecimal (uppercase). | (2) | +------------+-----------------------------------------------------+-------+ | 'e' | Floating-point exponential format (lowercase). | (3) | +------------+-----------------------------------------------------+-------+ | 'E' | Floating-point exponential format (uppercase). | (3) | +------------+-----------------------------------------------------+-------+ | 'f' | Floating-point decimal format. | (3) | +------------+-----------------------------------------------------+-------+ | 'F' | Floating-point decimal format. | (3) | +------------+-----------------------------------------------------+-------+ | 'g' | Floating-point format. Uses lowercase exponential | (4) | | | format if exponent is less than -4 or not less than | | | | precision, decimal format otherwise. | | +------------+-----------------------------------------------------+-------+ | 'G' | Floating-point format. Uses uppercase exponential | (4) | | | format if exponent is less than -4 or not less than | | | | precision, decimal format otherwise. | | +------------+-----------------------------------------------------+-------+ | 'c' | Single byte (accepts integer or single | | | | byte objects). | | +------------+-----------------------------------------------------+-------+ | 'b' | Bytes (any object that follows the | (5) | | | :ref:buffer protocol <bufferobjects> or has | | | | :meth:~object.__bytes__). | | +------------+-----------------------------------------------------+-------+ | 's' | 's' is an alias for 'b' and should only | (6) | | | be used for Python2/3 code bases. | | +------------+-----------------------------------------------------+-------+ | 'a' | Bytes (converts any Python object using | (5) | | | repr(obj).encode('ascii', 'backslashreplace')). | | +------------+-----------------------------------------------------+-------+ | 'r' | 'r' is an alias for 'a' and should only | (7) | | | be used for Python2/3 code bases. | | +------------+-----------------------------------------------------+-------+ | '%' | No argument is converted, results in a '%' | | | | character in the result. | | +------------+-----------------------------------------------------+-------+

Notes:

(1) The alternate form causes a leading octal specifier ('0o') to be inserted before the first digit.

(2) The alternate form causes a leading '0x' or '0X' (depending on whether the 'x' or 'X' format was used) to be inserted before the first digit.

(3) The alternate form causes the result to always contain a decimal point, even if no digits follow it.

The precision determines the number of digits after the decimal point and defaults to 6.

(4) The alternate form causes the result to always contain a decimal point, and trailing zeroes are not removed as they would otherwise be.

The precision determines the number of significant digits before and after the decimal point and defaults to 6.

(5) If precision is N, the output is truncated to N characters.

(6) b'%s' is deprecated, but will not be removed during the 3.x series.

(7) b'%r' is deprecated, but will not be removed during the 3.x series.

(8) See :pep:237.

.. note::

The bytearray version of this method does not operate in place - it always produces a new object, even if no changes were made.

.. seealso::

:pep:461 - Adding % formatting to bytes and bytearray

.. versionadded:: 3.5

.. _typememoryview:

Memory Views

:class:memoryview objects allow Python code to access the internal data of an object that supports the :ref:buffer protocol <bufferobjects> without copying.

.. class:: memoryview(object)

Create a :class:memoryview that references object. object must support the buffer protocol. Built-in objects that support the buffer protocol include :class:bytes and :class:bytearray.

A :class:memoryview has the notion of an element, which is the atomic memory unit handled by the originating object. For many simple types such as :class:bytes and :class:bytearray, an element is a single byte, but other types such as :class:array.array may have bigger elements.

len(view) is equal to the length of :meth:~memoryview.tolist, which is the nested list representation of the view. If view.ndim = 1, this is equal to the number of elements in the view.

.. versionchanged:: 3.12 If view.ndim == 0, len(view) now raises :exc:TypeError instead of returning 1.

The :class:~memoryview.itemsize attribute will give you the number of bytes in a single element.

A :class:memoryview supports slicing and indexing to expose its data. One-dimensional slicing will result in a subview::

>>> v = memoryview(b'abcefg')
>>> v[1]
98
>>> v[-1]
103
>>> v[1:4]
<memory at 0x7f3ddc9f4350>
>>> bytes(v[1:4])
b'bce'

If :class:~memoryview.format is one of the native format specifiers from the :mod:struct module, indexing with an integer or a tuple of integers is also supported and returns a single element with the correct type. One-dimensional memoryviews can be indexed with an integer or a one-integer tuple. Multi-dimensional memoryviews can be indexed with tuples of exactly ndim integers where ndim is the number of dimensions. Zero-dimensional memoryviews can be indexed with the empty tuple.

Here is an example with a non-byte format::

  >>> import array
  >>> a = array.array('l', [-11111111, 22222222, -33333333, 44444444])
  >>> m = memoryview(a)
  >>> m[0]
  -11111111
  >>> m[-1]
  44444444
  >>> m[::2].tolist()
  [-11111111, -33333333]

If the underlying object is writable, the memoryview supports one-dimensional slice assignment. Resizing is not allowed::

  >>> data = bytearray(b'abcefg')
  >>> v = memoryview(data)
  >>> v.readonly
  False
  >>> v[0] = ord(b'z')
  >>> data
  bytearray(b'zbcefg')
  >>> v[1:4] = b'123'
  >>> data
  bytearray(b'z123fg')
  >>> v[2:3] = b'spam'
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  ValueError: memoryview assignment: lvalue and rvalue have different structures
  >>> v[2:6] = b'spam'
  >>> data
  bytearray(b'z1spam')

One-dimensional memoryviews of :term:hashable (read-only) types with formats 'B', 'b' or 'c' are also hashable. The hash is defined as hash(m) == hash(m.tobytes())::

  >>> v = memoryview(b'abcefg')
  >>> hash(v) == hash(b'abcefg')
  True
  >>> hash(v[2:4]) == hash(b'ce')
  True
  >>> hash(v[::-2]) == hash(b'abcefg'[::-2])
  True

.. versionchanged:: 3.3 One-dimensional memoryviews can now be sliced. One-dimensional memoryviews with formats 'B', 'b' or 'c' are now :term:hashable.

.. versionchanged:: 3.4 memoryview is now registered automatically with :class:collections.abc.Sequence

.. versionchanged:: 3.5 memoryviews can now be indexed with tuple of integers.

.. versionchanged:: 3.14 memoryview is now a :term:generic type.

:class:memoryview has several methods:

.. method:: eq(exporter)

  A memoryview and a :pep:`3118` exporter are equal if their shapes are
  equivalent and if all corresponding values are equal when the operands'
  respective format codes are interpreted using :mod:`struct` syntax.

  For the subset of :mod:`struct` format strings currently supported by
  :meth:`tolist`, ``v`` and ``w`` are equal if ``v.tolist() == w.tolist()``::

     >>> import array
     >>> a = array.array('I', [1, 2, 3, 4, 5])
     >>> b = array.array('d', [1.0, 2.0, 3.0, 4.0, 5.0])
     >>> c = array.array('b', [5, 3, 1])
     >>> x = memoryview(a)
     >>> y = memoryview(b)
     >>> x == a == y == b
     True
     >>> x.tolist() == a.tolist() == y.tolist() == b.tolist()
     True
     >>> z = y[::-2]
     >>> z == c
     True
     >>> z.tolist() == c.tolist()
     True

  If either format string is not supported by the :mod:`struct` module,
  then the objects will always compare as unequal (even if the format
  strings and buffer contents are identical)::

     >>> from ctypes import BigEndianStructure, c_long
     >>> class BEPoint(BigEndianStructure):
     ...     _fields_ = [("x", c_long), ("y", c_long)]
     ...
     >>> point = BEPoint(100, 200)
     >>> a = memoryview(point)
     >>> b = memoryview(point)
     >>> a == point
     False
     >>> a == b
     False

  Note that, as with floating-point numbers, ``v is w`` does *not* imply
  ``v == w`` for memoryview objects.

  .. versionchanged:: 3.3
     Previous versions compared the raw memory disregarding the item format
     and the logical array structure.

.. method:: tobytes(order='C')

  Return the data in the buffer as a bytestring.  This is equivalent to
  calling the :class:`bytes` constructor on the memoryview. ::

     >>> m = memoryview(b"abc")
     >>> m.tobytes()
     b'abc'
     >>> bytes(m)
     b'abc'

  For non-contiguous arrays the result is equal to the flattened list
  representation with all elements converted to bytes. :meth:`tobytes`
  supports all format strings, including those that are not in
  :mod:`struct` module syntax.

  .. versionadded:: 3.8
     *order* can be {'C', 'F', 'A'}.  When *order* is 'C' or 'F', the data
     of the original array is converted to C or Fortran order. For contiguous
     views, 'A' returns an exact copy of the physical memory. In particular,
     in-memory Fortran order is preserved. For non-contiguous views, the
     data is converted to C first. *order=None* is the same as *order='C'*.

.. method:: hex(*, bytes_per_sep=1) hex(sep, bytes_per_sep=1)

  Return a string object containing two hexadecimal digits for each
  byte in the buffer. ::

     >>> m = memoryview(b"abc")
     >>> m.hex()
     '616263'

  .. versionadded:: 3.5

  .. versionchanged:: 3.8
     Similar to :meth:`bytes.hex`, :meth:`memoryview.hex` now supports
     optional *sep* and *bytes_per_sep* parameters to insert separators
     between bytes in the hex output.

.. method:: tolist()

  Return the data in the buffer as a list of elements. ::

     >>> memoryview(b'abc').tolist()
     [97, 98, 99]
     >>> import array
     >>> a = array.array('d', [1.1, 2.2, 3.3])
     >>> m = memoryview(a)
     >>> m.tolist()
     [1.1, 2.2, 3.3]

  .. versionchanged:: 3.3
     :meth:`tolist` now supports all single character native formats in
     :mod:`struct` module syntax as well as multi-dimensional
     representations.

.. method:: toreadonly()

  Return a readonly version of the memoryview object.  The original
  memoryview object is unchanged. ::

     >>> m = memoryview(bytearray(b'abc'))
     >>> mm = m.toreadonly()
     >>> mm.tolist()
     [97, 98, 99]
     >>> mm[0] = 42
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     TypeError: cannot modify read-only memory
     >>> m[0] = 43
     >>> mm.tolist()
     [43, 98, 99]

  .. versionadded:: 3.8

.. method:: release()

  Release the underlying buffer exposed by the memoryview object.  Many
  objects take special actions when a view is held on them (for example,
  a :class:`bytearray` would temporarily forbid resizing); therefore,
  calling release() is handy to remove these restrictions (and free any
  dangling resources) as soon as possible.

  After this method has been called, any further operation on the view
  raises a :class:`ValueError` (except :meth:`release` itself which can
  be called multiple times)::

     >>> m = memoryview(b'abc')
     >>> m.release()
     >>> m[0]
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ValueError: operation forbidden on released memoryview object

  The context management protocol can be used for a similar effect,
  using the ``with`` statement::

     >>> with memoryview(b'abc') as m:
     ...     m[0]
     ...
     97
     >>> m[0]
     Traceback (most recent call last):
       File "<stdin>", line 1, in <module>
     ValueError: operation forbidden on released memoryview object

  .. versionadded:: 3.2

.. method:: cast(format, /) cast(format, shape, /)

  Cast a memoryview to a new format or shape. *shape* defaults to
  ``[byte_length//new_itemsize]``, which means that the result view
  will be one-dimensional. The return value is a new memoryview, but
  the buffer itself is not copied. Supported casts are 1D -> C-:term:`contiguous`
  and C-contiguous -> 1D.

  The destination format is restricted to a single element native format in
  :mod:`struct` syntax. One of the formats must be a byte format
  ('B', 'b' or 'c'). The byte length of the result must be the same
  as the original length.
  Note that all byte lengths may depend on the operating system.

  Cast 1D/long to 1D/unsigned bytes::

     >>> import array
     >>> a = array.array('l', [1,2,3])
     >>> x = memoryview(a)
     >>> x.format
     'l'
     >>> x.itemsize
     8
     >>> len(x)
     3
     >>> x.nbytes
     24
     >>> y = x.cast('B')
     >>> y.format
     'B'
     >>> y.itemsize
     1
     >>> len(y)
     24
     >>> y.nbytes
     24

  Cast 1D/unsigned bytes to 1D/char::

     >>> b = bytearray(b'zyz')
     >>> x = memoryview(b)
     >>> x[0] = b'a'
     Traceback (most recent call last):
       ...
     TypeError: memoryview: invalid type for format 'B'
     >>> y = x.cast('c')
     >>> y[0] = b'a'
     >>> b
     bytearray(b'ayz')

  Cast 1D/bytes to 3D/ints to 1D/signed char::

     >>> import struct
     >>> buf = struct.pack("i"*12, *list(range(12)))
     >>> x = memoryview(buf)
     >>> y = x.cast('i', shape=[2,2,3])
     >>> y.tolist()
     [[[0, 1, 2], [3, 4, 5]], [[6, 7, 8], [9, 10, 11]]]
     >>> y.format
     'i'
     >>> y.itemsize
     4
     >>> len(y)
     2
     >>> y.nbytes
     48
     >>> z = y.cast('b')
     >>> z.format
     'b'
     >>> z.itemsize
     1
     >>> len(z)
     48
     >>> z.nbytes
     48

  Cast 1D/unsigned long to 2D/unsigned long::

     >>> buf = struct.pack("L"*6, *list(range(6)))
     >>> x = memoryview(buf)
     >>> y = x.cast('L', shape=[2,3])
     >>> len(y)
     2
     >>> y.nbytes
     48
     >>> y.tolist()
     [[0, 1, 2], [3, 4, 5]]

  .. versionadded:: 3.3

  .. versionchanged:: 3.5
     The source format is no longer restricted when casting to a byte view.

.. method:: count(value, /)

  Count the number of occurrences of *value*.

  .. versionadded:: 3.14

.. method:: index(value, start=0, stop=sys.maxsize, /)

  Return the index of the first occurrence of *value* (at or after
  index *start* and before index *stop*).

  Raises a :exc:`ValueError` if *value* cannot be found.

  .. versionadded:: 3.14

There are also several readonly attributes available:

.. attribute:: obj

  The underlying object of the memoryview::

     >>> b  = bytearray(b'xyz')
     >>> m = memoryview(b)
     >>> m.obj is b
     True

  .. versionadded:: 3.3

.. attribute:: nbytes

  ``nbytes == product(shape) * itemsize == len(m.tobytes())``. This is
  the amount of space in bytes that the array would use in a contiguous
  representation. It is not necessarily equal to ``len(m)``::

     >>> import array
     >>> a = array.array('i', [1,2,3,4,5])
     >>> m = memoryview(a)
     >>> len(m)
     5
     >>> m.nbytes
     20
     >>> y = m[::2]
     >>> len(y)
     3
     >>> y.nbytes
     12
     >>> len(y.tobytes())
     12

  Multi-dimensional arrays::

     >>> import struct
     >>> buf = struct.pack("d"*12, *[1.5*x for x in range(12)])
     >>> x = memoryview(buf)
     >>> y = x.cast('d', shape=[3,4])
     >>> y.tolist()
     [[0.0, 1.5, 3.0, 4.5], [6.0, 7.5, 9.0, 10.5], [12.0, 13.5, 15.0, 16.5]]
     >>> len(y)
     3
     >>> y.nbytes
     96

  .. versionadded:: 3.3

.. attribute:: readonly

  A bool indicating whether the memory is read only.

.. attribute:: format

  A string containing the format (in :mod:`struct` module style) for each
  element in the view. A memoryview can be created from exporters with
  arbitrary format strings, but some methods (e.g. :meth:`tolist`) are
  restricted to native single element formats.

  .. versionchanged:: 3.3
     format ``'B'`` is now handled according to the struct module syntax.
     This means that ``memoryview(b'abc')[0] == b'abc'[0] == 97``.

.. attribute:: itemsize

  The size in bytes of each element of the memoryview::

     >>> import array, struct
     >>> m = memoryview(array.array('H', [32000, 32001, 32002]))
     >>> m.itemsize
     2
     >>> m[0]
     32000
     >>> struct.calcsize('H') == m.itemsize
     True

.. attribute:: ndim

  An integer indicating how many dimensions of a multi-dimensional array the
  memory represents.

.. attribute:: shape

  A tuple of integers the length of :attr:`ndim` giving the shape of the
  memory as an N-dimensional array.

  .. versionchanged:: 3.3
     An empty tuple instead of ``None`` when ndim = 0.

.. attribute:: strides

  A tuple of integers the length of :attr:`ndim` giving the size in bytes to
  access each element for each dimension of the array.

  .. versionchanged:: 3.3
     An empty tuple instead of ``None`` when ndim = 0.

.. attribute:: suboffsets

  Used internally for PIL-style arrays. The value is informational only.

.. attribute:: c_contiguous

  A bool indicating whether the memory is C-:term:`contiguous`.

  .. versionadded:: 3.3

.. attribute:: f_contiguous

  A bool indicating whether the memory is Fortran :term:`contiguous`.

  .. versionadded:: 3.3

.. attribute:: contiguous

  A bool indicating whether the memory is :term:`contiguous`.

  .. versionadded:: 3.3

For information on the thread safety of :class:memoryview objects in the :term:free-threaded build, see :ref:thread-safety-memoryview.

.. _types-set:

Set Types --- :class:`set`, :class:`frozenset`

.. index:: pair: object; set

A :dfn:set object is an unordered collection of distinct :term:hashable objects. Common uses include membership testing, removing duplicates from a sequence, and computing mathematical operations such as intersection, union, difference, and symmetric difference. (For other containers see the built-in :class:dict, :class:list, and :class:tuple classes, and the :mod:collections module.)

Like other collections, sets support x in set, len(set), and for x in set. Being an unordered collection, sets do not record element position or order of insertion. Accordingly, sets do not support indexing, slicing, or other sequence-like behavior.

There are currently two built-in set types, :class:set and :class:frozenset. The :class:set type is mutable --- the contents can be changed using methods like :meth:~set.add and :meth:~set.remove. Since it is mutable, it has no hash value and cannot be used as either a dictionary key or as an element of another set. The :class:frozenset type is immutable and :term:hashable --- its contents cannot be altered after it is created; it can therefore be used as a dictionary key or as an element of another set.

Non-empty sets (not frozensets) can be created by placing a comma-separated list of elements within braces, for example: {'jack', 'sjoerd'}, in addition to the :class:set constructor.

The constructors for both classes work the same:

.. class:: set(iterable=(), /) frozenset(iterable=(), /)

Return a new set or frozenset object whose elements are taken from iterable. The elements of a set must be :term:hashable. To represent sets of sets, the inner sets must be :class:frozenset objects. If iterable is not specified, a new empty set is returned.

Sets can be created by several means:

Use a comma-separated list of elements within braces: {'jack', 'sjoerd'}
Use a set comprehension: {c for c in 'abracadabra' if c not in 'abc'}
Use the type constructor: set(), set('foobar'), set(['a', 'b', 'foo'])

Instances of :class:set and :class:frozenset provide the following operations:

.. describe:: len(s)

Return the number of elements in set s (cardinality of s).

.. describe:: x in s

Test x for membership in s.

.. describe:: x not in s

Test x for non-membership in s.

.. method:: frozenset.isdisjoint(other, /) set.isdisjoint(other, /)

Return True if the set has no elements in common with other. Sets are disjoint if and only if their intersection is the empty set.

.. method:: frozenset.issubset(other, /) set.issubset(other, /) .. describe:: set <= other

Test whether every element in the set is in other.

.. describe:: set < other

Test whether the set is a proper subset of other, that is, set <= other and set != other.

.. method:: frozenset.issuperset(other, /) set.issuperset(other, /) .. describe:: set >= other

Test whether every element in other is in the set.

.. describe:: set > other

Test whether the set is a proper superset of other, that is, set >= other and set != other.

.. method:: frozenset.union(*others) set.union(*others) .. describe:: set | other | ...

Return a new set with elements from the set and all others.

.. method:: frozenset.intersection(*others) set.intersection(*others) .. describe:: set & other & ...

Return a new set with elements common to the set and all others.

.. method:: frozenset.difference(*others) set.difference(*others) .. describe:: set - other - ...

Return a new set with elements in the set that are not in the others.

.. method:: frozenset.symmetric_difference(other, /) set.symmetric_difference(other, /) .. describe:: set ^ other

Return a new set with elements in either the set or other but not both.

.. method:: frozenset.copy() set.copy()

Return a shallow copy of the set.

Note, the non-operator versions of :meth:~frozenset.union, :meth:~frozenset.intersection, :meth:~frozenset.difference, :meth:~frozenset.symmetric_difference, :meth:~frozenset.issubset, and :meth:~frozenset.issuperset methods will accept any iterable as an argument. In contrast, their operator based counterparts require their arguments to be sets. This precludes error-prone constructions like set('abc') & 'cbs' in favor of the more readable set('abc').intersection('cbs').

Both :class:set and :class:frozenset support set to set comparisons. Two sets are equal if and only if every element of each set is contained in the other (each is a subset of the other). A set is less than another set if and only if the first set is a proper subset of the second set (is a subset, but is not equal). A set is greater than another set if and only if the first set is a proper superset of the second set (is a superset, but is not equal).

Instances of :class:set are compared to instances of :class:frozenset based on their members. For example, set('abc') == frozenset('abc') returns True and so does set('abc') in set([frozenset('abc')]).

The subset and equality comparisons do not generalize to a total ordering function. For example, any two nonempty disjoint sets are not equal and are not subsets of each other, so all of the following return False: a<b, a==b, or a>b.

Since sets only define partial ordering (subset relationships), the output of the :meth:list.sort method is undefined for lists of sets.

Set elements, like dictionary keys, must be :term:hashable.

Binary operations that mix :class:set instances with :class:frozenset return the type of the first operand. For example: frozenset('ab') | set('bc') returns an instance of :class:frozenset.

The following table lists operations available for :class:set that do not apply to immutable instances of :class:frozenset:

.. method:: set.update(*others) .. describe:: set |= other | ...

Update the set, adding elements from all others.

.. method:: set.intersection_update(*others) .. describe:: set &= other & ...

Update the set, keeping only elements found in it and all others.

.. method:: set.difference_update(*others) .. describe:: set -= other | ...

Update the set, removing elements found in others.

.. method:: set.symmetric_difference_update(other, /) .. describe:: set ^= other

Update the set, keeping only elements found in either set, but not in both.

.. method:: set.add(elem, /)

Add element elem to the set.

.. method:: set.remove(elem, /)

Remove element elem from the set. Raises :exc:KeyError if elem is not contained in the set.

.. method:: set.discard(elem, /)

Remove element elem from the set if it is present.

.. method:: set.pop()

Remove and return an arbitrary element from the set. Raises :exc:KeyError if the set is empty.

.. method:: set.clear()

Remove all elements from the set.

Note, the non-operator versions of the :meth:~set.update, :meth:~set.intersection_update, :meth:~set.difference_update, and :meth:~set.symmetric_difference_update methods will accept any iterable as an argument.

Note, the elem argument to the :meth:~object.__contains__, :meth:~set.remove, and :meth:~set.discard methods may be a set. To support searching for an equivalent frozenset, a temporary one is created from elem.

.. seealso::

For detailed information on thread-safety guarantees for :class:set objects, see :ref:thread-safety-set.

.. _typesmapping:

Mapping types --- :class:`!dict`, :class:`!frozendict`

.. index:: pair: object; mapping pair: object; dictionary triple: operations on; mapping; types triple: operations on; dictionary; type pair: statement; del pair: built-in function; len

A :term:mapping object maps :term:hashable values to arbitrary objects. There are currently two standard mapping types, the :dfn:dictionary and :class:frozendict. (For other containers see the built-in :class:list, :class:set, and :class:tuple classes, and the :mod:collections module.)

A dictionary's keys are almost arbitrary values. Values that are not :term:hashable, that is, values containing lists, dictionaries or other mutable types (that are compared by value rather than by object identity) may not be used as keys. Values that compare equal (such as 1, 1.0, and True) can be used interchangeably to index the same dictionary entry.

.. class:: dict(**kwargs) dict(mapping, /, **kwargs) dict(iterable, /, **kwargs)

Return a new dictionary initialized from an optional positional argument and a possibly empty set of keyword arguments.

Dictionaries can be created by several means:

Use a comma-separated list of key: value pairs within braces: {'jack': 4098, 'sjoerd': 4127} or {4098: 'jack', 4127: 'sjoerd'}
Use a dict comprehension: {}, {x: x ** 2 for x in range(10)}
Use the type constructor: dict(), dict([('foo', 100), ('bar', 200)]), dict(foo=100, bar=200)

If no positional argument is given, an empty dictionary is created. If a positional argument is given and it defines a keys() method, a dictionary is created by calling :meth:~object.__getitem__ on the argument with each returned key from the method. Otherwise, the positional argument must be an :term:iterable object. Each item in the iterable must itself be an iterable with exactly two elements. The first element of each item becomes a key in the new dictionary, and the second element the corresponding value. If a key occurs more than once, the last value for that key becomes the corresponding value in the new dictionary.

If keyword arguments are given, the keyword arguments and their values are added to the dictionary created from the positional argument. If a key being added is already present, the value from the keyword argument replaces the value from the positional argument.

Dictionaries compare equal if and only if they have the same (key, value) pairs (regardless of ordering). Order comparisons ('<', '<=', '>=', '>') raise :exc:TypeError. To illustrate dictionary creation and equality, the following examples all return a dictionary equal to {"one": 1, "two": 2, "three": 3}::

  >>> a = dict(one=1, two=2, three=3)
  >>> b = {'one': 1, 'two': 2, 'three': 3}
  >>> c = dict(zip(['one', 'two', 'three'], [1, 2, 3]))
  >>> d = dict([('two', 2), ('one', 1), ('three', 3)])
  >>> e = dict({'three': 3, 'one': 1, 'two': 2})
  >>> f = dict({'one': 1, 'three': 3}, two=2)
  >>> a == b == c == d == e == f
  True

Providing keyword arguments as in the first example only works for keys that are valid Python identifiers. Otherwise, any valid keys can be used.

Dictionaries preserve insertion order. Note that updating a key does not affect the order. Keys added after deletion are inserted at the end. ::

  >>> d = {"one": 1, "two": 2, "three": 3, "four": 4}
  >>> d
  {'one': 1, 'two': 2, 'three': 3, 'four': 4}
  >>> list(d)
  ['one', 'two', 'three', 'four']
  >>> list(d.values())
  [1, 2, 3, 4]
  >>> d["one"] = 42
  >>> d
  {'one': 42, 'two': 2, 'three': 3, 'four': 4}
  >>> del d["two"]
  >>> d["two"] = None
  >>> d
  {'one': 42, 'three': 3, 'four': 4, 'two': None}

.. versionchanged:: 3.7 Dictionary order is guaranteed to be insertion order. This behavior was an implementation detail of CPython from 3.6.

These are the operations that dictionaries support (and therefore, custom mapping types should support too):

.. describe:: list(d)

  Return a list of all the keys used in the dictionary *d*.

.. describe:: len(d)

  Return the number of items in the dictionary *d*.

.. describe:: d[key]

  Return the item of *d* with key *key*.  Raises a :exc:`KeyError` if *key* is
  not in the map.

  .. index:: __missing__()

  If a subclass of dict defines a method :meth:`~object.__missing__` and *key*
  is not present, the ``d[key]`` operation calls that method with the key *key*
  as argument.  The ``d[key]`` operation then returns or raises whatever is
  returned or raised by the ``__missing__(key)`` call.
  No other operations or methods invoke :meth:`~object.__missing__`. If
  :meth:`~object.__missing__` is not defined, :exc:`KeyError` is raised.
  :meth:`~object.__missing__` must be a method; it cannot be an instance variable::

      >>> class Counter(dict):
      ...     def __missing__(self, key):
      ...         return 0
      ...
      >>> c = Counter()
      >>> c['red']
      0
      >>> c['red'] += 1
      >>> c['red']
      1

  The example above shows part of the implementation of
  :class:`collections.Counter`.
  A different :meth:`!__missing__` method is used
  by :class:`collections.defaultdict`.

.. describe:: d[key] = value

  Set ``d[key]`` to *value*.

.. describe:: del d[key]

  Remove ``d[key]`` from *d*.  Raises a :exc:`KeyError` if *key* is not in the
  map.

.. describe:: key in d

  Return ``True`` if *d* has a key *key*, else ``False``.

.. describe:: key not in d

  Equivalent to ``not key in d``.

.. describe:: iter(d)

  Return an iterator over the keys of the dictionary.  This is a shortcut
  for ``iter(d.keys())``.

.. method:: clear()

  Remove all items from the dictionary.

.. method:: copy()

  Return a shallow copy of the dictionary.

.. classmethod:: fromkeys(iterable, value=None, /)

  Create a new dictionary with keys from *iterable* and values set to *value*.

  :meth:`fromkeys` is a class method that returns a new dictionary. *value*
  defaults to ``None``.  All of the values refer to just a single instance,
  so it generally doesn't make sense for *value* to be a mutable object
  such as an empty list.  To get distinct values, use a :ref:`dict
  comprehension <dict>` instead.

.. method:: get(key, default=None, /)

  Return the value for *key* if *key* is in the dictionary, else *default*.
  If *default* is not given, it defaults to ``None``, so that this method
  never raises a :exc:`KeyError`.

.. method:: items()

  Return a new view of the dictionary's items (``(key, value)`` pairs).
  See the :ref:`documentation of view objects <dict-views>`.

.. method:: keys()

  Return a new view of the dictionary's keys.  See the :ref:`documentation
  of view objects <dict-views>`.

.. method:: pop(key, /) pop(key, default, /)

  If *key* is in the dictionary, remove it and return its value, else return
  *default*.  If *default* is not given and *key* is not in the dictionary,
  a :exc:`KeyError` is raised.

.. method:: popitem()

  Remove and return a ``(key, value)`` pair from the dictionary.
  Pairs are returned in :abbr:`LIFO (last-in, first-out)` order.

  :meth:`popitem` is useful to destructively iterate over a dictionary, as
  often used in set algorithms.  If the dictionary is empty, calling
  :meth:`popitem` raises a :exc:`KeyError`.

  .. versionchanged:: 3.7
     LIFO order is now guaranteed. In prior versions, :meth:`popitem` would
     return an arbitrary key/value pair.

.. describe:: reversed(d)

  Return a reverse iterator over the keys of the dictionary. This is a
  shortcut for ``reversed(d.keys())``.

  .. versionadded:: 3.8

.. method:: setdefault(key, default=None, /)

  If *key* is in the dictionary, return its value.  If not, insert *key*
  with a value of *default* and return *default*.  *default* defaults to
  ``None``.

.. method:: update(**kwargs) update(mapping, /, **kwargs) update(iterable, /, **kwargs)

  Update the dictionary with the key/value pairs from *mapping* or *iterable* and *kwargs*, overwriting
  existing keys.  Return ``None``.

  :meth:`update` accepts either another object with a ``keys()`` method (in
  which case :meth:`~object.__getitem__` is called with every key returned from
  the method) or an iterable of key/value pairs (as tuples or other iterables
  of length two). If keyword arguments are specified, the dictionary is then
  updated with those key/value pairs: ``d.update(red=1, blue=2)``.

.. method:: values()

  Return a new view of the dictionary's values.  See the
  :ref:`documentation of view objects <dict-views>`.

  An equality comparison between one ``dict.values()`` view and another
  will always return ``False``. This also applies when comparing
  ``dict.values()`` to itself::

     >>> d = {'a': 1}
     >>> d.values() == d.values()
     False

.. describe:: d | other

  Create a new dictionary with the merged keys and values of *d* and
  *other*, which must both be dictionaries. The values of *other* take
  priority when *d* and *other* share keys.

  .. versionadded:: 3.9

.. describe:: d |= other

  Update the dictionary *d* with keys and values from *other*, which may be
  either a :term:`mapping` or an :term:`iterable` of key/value pairs. The
  values of *other* take priority when *d* and *other* share keys.

  .. versionadded:: 3.9

Dictionaries and dictionary views are reversible. ::

  >>> d = {"one": 1, "two": 2, "three": 3, "four": 4}
  >>> d
  {'one': 1, 'two': 2, 'three': 3, 'four': 4}
  >>> list(reversed(d))
  ['four', 'three', 'two', 'one']
  >>> list(reversed(d.values()))
  [4, 3, 2, 1]
  >>> list(reversed(d.items()))
  [('four', 4), ('three', 3), ('two', 2), ('one', 1)]

.. versionchanged:: 3.8 Dictionaries are now reversible.

.. seealso:: :class:frozendict and :class:types.MappingProxyType can be used to create a read-only view of a :class:dict.

.. seealso::

For detailed information on thread-safety guarantees for :class:dict objects, see :ref:thread-safety-dict.

.. _dict-views:

Dictionary view objects

The objects returned by :meth:dict.keys, :meth:dict.values and :meth:dict.items are view objects. They provide a dynamic view on the dictionary's entries, which means that when the dictionary changes, the view reflects these changes.

Dictionary views can be iterated over to yield their respective data, and support membership tests:

.. describe:: len(dictview)

Return the number of entries in the dictionary.

.. describe:: iter(dictview)

Return an iterator over the keys, values or items (represented as tuples of (key, value)) in the dictionary.

Keys and values are iterated over in insertion order. This allows the creation of (value, key) pairs using :func:zip: pairs = zip(d.values(), d.keys()). Another way to create the same list is pairs = [(v, k) for (k, v) in d.items()].

Iterating views while adding or deleting entries in the dictionary may raise a :exc:RuntimeError or fail to iterate over all entries.

.. versionchanged:: 3.7 Dictionary order is guaranteed to be insertion order.

.. describe:: x in dictview

Return True if x is in the underlying dictionary's keys, values or items (in the latter case, x should be a (key, value) tuple).

.. describe:: reversed(dictview)

Return a reverse iterator over the keys, values or items of the dictionary. The view will be iterated in reverse order of the insertion.

.. versionchanged:: 3.8 Dictionary views are now reversible.

.. describe:: dictview.mapping

Return a :class:types.MappingProxyType that wraps the original dictionary to which the view refers.

.. versionadded:: 3.10

Keys views are set-like since their entries are unique and :term:hashable. Items views also have set-like operations since the (key, value) pairs are unique and the keys are hashable. If all values in an items view are hashable as well, then the items view can interoperate with other sets. (Values views are not treated as set-like since the entries are generally not unique.) For set-like views, all of the operations defined for the abstract base class :class:collections.abc.Set are available (for example, ==, <, or ^). While using set operators, set-like views accept any iterable as the other operand, unlike sets which only accept sets as the input.

An example of dictionary view usage::

dishes = {'eggs': 2, 'sausage': 1, 'bacon': 1, 'spam': 500} keys = dishes.keys() values = dishes.values()

iteration

n = 0 for val in values: ... n += val ... print(n) 504

keys and values are iterated over in the same order (insertion order)

list(keys) ['eggs', 'sausage', 'bacon', 'spam'] list(values) [2, 1, 1, 500]

view objects are dynamic and reflect dict changes

del dishes['eggs'] del dishes['sausage'] list(keys) ['bacon', 'spam']

set operations

keys & {'eggs', 'bacon', 'salad'} {'bacon'} keys ^ {'sausage', 'juice'} == {'juice', 'sausage', 'bacon', 'spam'} True keys | ['juice', 'juice', 'juice'] == {'bacon', 'spam', 'juice'} True

get back a read-only proxy for the original dictionary

values.mapping mappingproxy({'bacon': 1, 'spam': 500}) values.mapping['spam'] 500

Frozen dictionaries

.. class:: frozendict(**kwargs) frozendict(mapping, /, **kwargs) frozendict(iterable, /, **kwargs)

Return a new frozen dictionary initialized from an optional positional argument and a possibly empty set of keyword arguments.

A :class:!frozendict has a similar API to the :class:dict API, with the following differences:

:class:!dict has more methods than :class:!frozendict:
- :meth:!__delitem__
- :meth:!__setitem__
- :meth:~dict.clear
- :meth:~dict.pop
- :meth:~dict.popitem
- :meth:~dict.setdefault
- :meth:~dict.update
A :class:!frozendict can be hashed with hash(frozendict) if all keys and values can be hashed.
frozendict |= other does not modify the :class:!frozendict in-place but creates a new frozen dictionary.

:class:!frozendict is not a :class:!dict subclass but inherits directly from object.

.. versionadded:: 3.15

.. _typecontextmanager:

Context Manager Types

.. index:: single: context manager single: context management protocol single: protocol; context management

Python's :keyword:with statement supports the concept of a runtime context defined by a context manager. This is implemented using a pair of methods that allow user-defined classes to define a runtime context that is entered before the statement body is executed and exited when the statement ends:

.. method:: contextmanager.enter()

Enter the runtime context and return either this object or another object related to the runtime context. The value returned by this method is bound to the identifier in the :keyword:!as clause of :keyword:with statements using this context manager.

An example of a context manager that returns itself is a :term:file object. File objects return themselves from enter() to allow :func:open to be used as the context expression in a :keyword:with statement.

An example of a context manager that returns a related object is the one returned by :func:decimal.localcontext. These managers set the active decimal context to a copy of the original decimal context and then return the copy. This allows changes to be made to the current decimal context in the body of the :keyword:with statement without affecting code outside the :keyword:!with statement.

.. method:: contextmanager.exit(exc_type, exc_val, exc_tb)

Exit the runtime context and return a Boolean flag indicating if any exception that occurred should be suppressed. If an exception occurred while executing the body of the :keyword:with statement, the arguments contain the exception type, value and traceback information. Otherwise, all three arguments are None.

Returning a true value from this method will cause the :keyword:with statement to suppress the exception and continue execution with the statement immediately following the :keyword:!with statement. Otherwise the exception continues propagating after this method has finished executing.

If this method raises an exception while handling an earlier exception from the :keyword:with block, the new exception is raised, and the original exception is stored in its :attr:~BaseException.__context__ attribute.

The exception passed in should never be reraised explicitly - instead, this method should return a false value to indicate that the method completed successfully and does not want to suppress the raised exception. This allows context management code to easily detect whether or not an :meth:~object.__exit__ method has actually failed.

Python defines several context managers to support easy thread synchronisation, prompt closure of files or other objects, and simpler manipulation of the active decimal arithmetic context. The specific types are not treated specially beyond their implementation of the context management protocol. See the :mod:contextlib module for some examples.

Python's :term:generator\s and the :class:contextlib.contextmanager decorator provide a convenient way to implement these protocols. If a generator function is decorated with the :class:contextlib.contextmanager decorator, it will return a context manager implementing the necessary :meth:~contextmanager.__enter__ and :meth:~contextmanager.__exit__ methods, rather than the iterator produced by an undecorated generator function.

Note that there is no specific slot for any of these methods in the type structure for Python objects in the Python/C API. Extension types wanting to define these methods must provide them as a normal Python accessible method. Compared to the overhead of setting up the runtime context, the overhead of a single class dictionary lookup is negligible.

Type Annotation Types --- :ref:`Generic Alias <types-genericalias>`, :ref:`Union <types-union>`

.. index:: single: annotation; type annotation; type hint

The core built-in types for :term:type annotations <annotation> are :ref:Generic Alias <types-genericalias> and :ref:Union <types-union>.

.. _types-genericalias:

Generic Alias Type

.. index:: pair: object; GenericAlias pair: Generic; Alias

GenericAlias objects are generally created by :ref:subscripting <subscriptions> a class. They are most often used with :ref:container classes <sequence-types>, such as :class:list or :class:dict. For example, list[int] is a GenericAlias object created by subscripting the list class with the argument :class:int. GenericAlias objects are intended primarily for use with :term:type annotations <annotation>.

.. note::

It is generally only possible to subscript a class if the class implements the special method :meth:~object.__class_getitem__.

A GenericAlias object acts as a proxy for a :term:generic type, implementing parameterized generics.

For a container class, the argument(s) supplied to a :ref:subscription <subscriptions> of the class may indicate the type(s) of the elements an object contains. For example, set[bytes] can be used in type annotations to signify a :class:set in which all the elements are of type :class:bytes.

For a class which defines :meth:~object.__class_getitem__ but is not a container, the argument(s) supplied to a subscription of the class will often indicate the return type(s) of one or more methods defined on an object. For example, :mod:regular expressions <re> can be used on both the :class:str data type and the :class:bytes data type:

If x = re.search('foo', 'foo'), x will be a :ref:re.Match <match-objects> object where the return values of x.group(0) and x[0] will both be of type :class:str. We can represent this kind of object in type annotations with the GenericAlias re.Match[str].
If y = re.search(b'bar', b'bar'), (note the b for :class:bytes), y will also be an instance of re.Match, but the return values of y.group(0) and y[0] will both be of type :class:bytes. In type annotations, we would represent this variety of :ref:re.Match <match-objects> objects with re.Match[bytes].

GenericAlias objects are instances of the class :class:types.GenericAlias, which can also be used to create GenericAlias objects directly.

.. describe:: T[X, Y, ...]

Creates a GenericAlias representing a type T parameterized by types X, Y, and more depending on the T used. For example, a function expecting a :class:list containing :class:float elements::

  def average(values: list[float]) -> float:
      return sum(values) / len(values)

Another example for :term:mapping objects, using a :class:dict, which is a generic type expecting two type parameters representing the key type and the value type. In this example, the function expects a dict with keys of type :class:str and values of type :class:int::

  def send_post_request(url: str, body: dict[str, int]) -> None:
      ...

The builtin functions :func:isinstance and :func:issubclass do not accept GenericAlias types for their second argument::

isinstance([1, 2], list[str]) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: isinstance() argument 2 cannot be a parameterized generic

The Python runtime does not enforce :term:type annotations <annotation>. This extends to generic types and their type parameters. When creating a container object from a GenericAlias, the elements in the container are not checked against their type. For example, the following code is discouraged, but will run without errors::

t = list[str] t([1, 2, 3]) [1, 2, 3]

Furthermore, parameterized generics erase type parameters during object creation::

t = list[str] type(t) <class 'types.GenericAlias'>

l = t() type(l) <class 'list'>

Calling :func:repr or :func:str on a generic shows the parameterized type::

repr(list[int]) 'list[int]'

str(list[int]) 'list[int]'

The :meth:~object.__getitem__ method of generic containers will raise an exception to disallow mistakes like dict[str][str]::

dict[str][str] Traceback (most recent call last): ... TypeError: dict[str] is not a generic class

However, such expressions are valid when :ref:type variables <generics> are used. The index must have as many elements as there are type variable items in the GenericAlias object's :attr:~genericalias.__args__. ::

from typing import TypeVar Y = TypeVar('Y') dict[str, Y][int] dict[str, int]

Standard Generic Classes ^^^^^^^^^^^^^^^^^^^^^^^^

The following standard library classes support parameterized generics. This list is non-exhaustive.

:class:tuple
:class:list
:class:dict
:class:set
:class:frozendict
:class:frozenset
:class:type
:class:asyncio.Future
:class:asyncio.Task
:class:collections.deque
:class:collections.defaultdict
:class:collections.OrderedDict
:class:collections.Counter
:class:collections.ChainMap
:class:collections.abc.Awaitable
:class:collections.abc.Coroutine
:class:collections.abc.AsyncIterable
:class:collections.abc.AsyncIterator
:class:collections.abc.AsyncGenerator
:class:collections.abc.Iterable
:class:collections.abc.Iterator
:class:collections.abc.Generator
:class:collections.abc.Reversible
:class:collections.abc.Container
:class:collections.abc.Collection
:class:collections.abc.Callable
:class:collections.abc.Set
:class:collections.abc.MutableSet
:class:collections.abc.Mapping
:class:collections.abc.MutableMapping
:class:collections.abc.Sequence
:class:collections.abc.MutableSequence
:class:collections.abc.ByteString
:class:collections.abc.MappingView
:class:collections.abc.KeysView
:class:collections.abc.ItemsView
:class:collections.abc.ValuesView
:class:contextlib.AbstractContextManager
:class:contextlib.AbstractAsyncContextManager
:class:dataclasses.Field
:class:functools.cached_property
:class:functools.partialmethod
:class:os.PathLike
:class:queue.LifoQueue
:class:queue.Queue
:class:queue.PriorityQueue
:class:queue.SimpleQueue
:ref:re.Pattern <re-objects>
:ref:re.Match <match-objects>
:class:shelve.BsdDbShelf
:class:shelve.DbfilenameShelf
:class:shelve.Shelf
:class:types.MappingProxyType
:class:weakref.WeakKeyDictionary
:class:weakref.WeakMethod
:class:weakref.WeakSet
:class:weakref.WeakValueDictionary

Special Attributes of GenericAlias objects ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

All parameterized generics implement special read-only attributes.

.. attribute:: genericalias.origin

This attribute points at the non-parameterized generic class::

  >>> list[int].__origin__
  <class 'list'>

.. attribute:: genericalias.args

This attribute is a :class:tuple (possibly of length 1) of generic types passed to the original :meth:~object.__class_getitem__ of the generic class::

  >>> dict[str, list[int]].__args__
  (<class 'str'>, list[int])

.. attribute:: genericalias.parameters

This attribute is a lazily computed tuple (possibly empty) of unique type variables found in __args__::

  >>> from typing import TypeVar

  >>> T = TypeVar('T')
  >>> list[T].__parameters__
  (~T,)

.. note:: A GenericAlias object with :class:typing.ParamSpec parameters may not have correct __parameters__ after substitution because :class:typing.ParamSpec is intended primarily for static type checking.

.. attribute:: genericalias.unpacked

A boolean that is true if the alias has been unpacked using the * operator (see :data:~typing.TypeVarTuple).

.. versionadded:: 3.11

.. seealso::

:pep:484 - Type Hints Introducing Python's framework for type annotations.

:pep:585 - Type Hinting Generics In Standard Collections Introducing the ability to natively parameterize standard-library classes, provided they implement the special class method :meth:~object.__class_getitem__.

:ref:Generics, :ref:user-defined generics <user-defined-generics> and :class:typing.Generic Documentation on how to implement generic classes that can be parameterized at runtime and understood by static type-checkers.

.. versionadded:: 3.9

.. _types-union:

Union Type

.. index:: pair: object; Union pair: union; type

A union object holds the value of the | (bitwise or) operation on multiple :ref:type objects <bltin-type-objects>. These types are intended primarily for :term:type annotations <annotation>. The union type expression enables cleaner type hinting syntax compared to subscripting :class:typing.Union.

.. describe:: X | Y | ...

Defines a union object which holds types X, Y, and so forth. X | Y means either X or Y. It is equivalent to typing.Union[X, Y]. For example, the following function expects an argument of type :class:int or :class:float::

  def square(number: int | float) -> int | float:
      return number ** 2

.. note::

  The ``|`` operand cannot be used at runtime to define unions where one or
  more members is a forward reference. For example, ``int | "Foo"``, where
  ``"Foo"`` is a reference to a class not yet defined, will fail at
  runtime. For unions which include forward references, present the
  whole expression as a string, e.g. ``"int | Foo"``.

.. describe:: union_object == other

Union objects can be tested for equality with other union objects. Details:

Unions of unions are flattened::

(int | str) | float == int | str | float
Redundant types are removed::

int | str | int == int | str
When comparing unions, the order is ignored::

int | str == str | int
It creates instances of :class:typing.Union::

int | str == typing.Union[int, str] type(int | str) is typing.Union
Optional types can be spelled as a union with None::

str | None == typing.Optional[str]

.. describe:: isinstance(obj, union_object) .. describe:: issubclass(obj, union_object)

Calls to :func:isinstance and :func:issubclass are also supported with a union object::

  >>> isinstance("", int | str)
  True

However, :ref:parameterized generics <types-genericalias> in union objects cannot be checked::

  >>> isinstance(1, int | list[int])  # short-circuit evaluation
  True
  >>> isinstance([1], int | list[int])
  Traceback (most recent call last):
    ...
  TypeError: isinstance() argument 2 cannot be a parameterized generic

The user-exposed type for the union object can be accessed from :class:typing.Union and used for :func:isinstance checks::

import typing isinstance(int | str, typing.Union) True typing.Union() Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: cannot create 'typing.Union' instances

.. note:: The :meth:!__or__ method for type objects was added to support the syntax X | Y. If a metaclass implements :meth:!__or__, the Union may override it:

.. doctest::

  >>> class M(type):
  ...     def __or__(self, other):
  ...         return "Hello"
  ...
  >>> class C(metaclass=M):
  ...     pass
  ...
  >>> C | int
  'Hello'
  >>> int | C
  int | C

.. seealso::

:pep:604 -- PEP proposing the X | Y syntax and the Union type.

.. versionadded:: 3.10

.. versionchanged:: 3.14

Union objects are now instances of :class:typing.Union. Previously, they were instances of :class:types.UnionType, which remains an alias for :class:typing.Union.

.. _typesother:

Other Built-in Types

The interpreter supports several other kinds of objects. Most of these support only one or two operations.

.. _typesmodules:

Modules

The only special operation on a module is attribute access: m.name, where m is a module and name accesses a name defined in m's symbol table. Module attributes can be assigned to. (Note that the :keyword:import statement is not, strictly speaking, an operation on a module object; import foo does not require a module object named foo to exist, rather it requires an (external) definition for a module named foo somewhere.)

A special attribute of every module is :attr:~object.__dict__. This is the dictionary containing the module's symbol table. Modifying this dictionary will actually change the module's symbol table, but direct assignment to the :attr:~object.__dict__ attribute is not possible (you can write m.__dict__['a'] = 1, which defines m.a to be 1, but you can't write m.__dict__ = {}). Modifying :attr:~object.__dict__ directly is not recommended.

Modules built into the interpreter are written like this: <module 'sys' (built-in)>. If loaded from a file, they are written as <module 'os' from '/usr/local/lib/pythonX.Y/os.pyc'>.

.. _typesobjects:

Classes and Class Instances

See :ref:objects and :ref:class for these.

.. _typesfunctions:

Functions

Function objects are created by function definitions. The only operation on a function object is to call it: func(argument-list).

There are really two flavors of function objects: built-in functions and user-defined functions. Both support the same operation (to call the function), but the implementation is different, hence the different object types.

See :ref:function for more information.

.. _typesmethods:

Methods

.. index:: pair: object; method

Methods are functions that are called using the attribute notation. There are two flavors: :ref:built-in methods <builtin-methods> (such as :meth:~list.append on lists) and :ref:class instance method <instance-methods>. Built-in methods are described with the types that support them.

If you access a method (a function defined in a class namespace) through an instance, you get a special object: a :dfn:bound method (also called :ref:instance method <instance-methods>) object. When called, it will add the self argument to the argument list. Bound methods have two special read-only attributes: :attr:m.__self__ <method.__self__> is the object on which the method operates, and :attr:m.__func__ <method.__func__> is the function implementing the method. Calling m(arg-1, arg-2, ..., arg-n) is completely equivalent to calling m.__func__(m.__self__, arg-1, arg-2, ..., arg-n).

Like :ref:function objects <user-defined-funcs>, bound method objects support getting arbitrary attributes. However, since method attributes are actually stored on the underlying function object (:attr:method.__func__), setting method attributes on bound methods is disallowed. Attempting to set an attribute on a method results in an :exc:AttributeError being raised. In order to set a method attribute, you need to explicitly set it on the underlying function object:

.. doctest::

class C: ... def method(self): ... pass ... c = C() c.method.whoami = 'my name is method' # can't set on the method Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'method' object has no attribute 'whoami' c.method.func.whoami = 'my name is method' c.method.whoami 'my name is method'

See :ref:instance-methods for more information.

.. index:: object; code, code object

.. _bltin-code-objects:

Code Objects

.. index:: pair: built-in function; compile single: code (function object attribute)

Code objects are used by the implementation to represent "pseudo-compiled" executable Python code such as a function body. They differ from function objects because they don't contain a reference to their global execution environment. Code objects are returned by the built-in :func:compile function and can be extracted from function objects through their :attr:~function.__code__ attribute. See also the :mod:code module.

Accessing :attr:~function.__code__ raises an :ref:auditing event <auditing> object.__getattr__ with arguments obj and "__code__".

.. index:: pair: built-in function; exec pair: built-in function; eval

A code object can be executed or evaluated by passing it (instead of a source string) to the :func:exec or :func:eval built-in functions.

See :ref:types for more information.

.. _bltin-type-objects:

Type Objects

.. index:: pair: built-in function; type pair: module; types

Type objects represent the various object types. An object's type is accessed by the built-in function :func:type. There are no special operations on types. The standard module :mod:types defines names for all standard built-in types.

Types are written like this: <class 'int'>.

.. _bltin-null-object:

The Null Object

This object is returned by functions that don't explicitly return a value. It supports no special operations. There is exactly one null object, named None (a built-in name). type(None)() produces the same singleton.

It is written as None.

.. index:: single: ...; ellipsis literal .. _bltin-ellipsis-object:

The Ellipsis Object

This object is commonly used to indicate that something is omitted. It supports no special operations. There is exactly one ellipsis object, named :const:Ellipsis (a built-in name). type(Ellipsis)() produces the :const:Ellipsis singleton.

It is written as Ellipsis or ....

In typical use, ... as the Ellipsis object appears in a few different places, for instance:

In type annotations, such as :ref:callable arguments <annotating-callables> or :ref:tuple elements <annotating-tuples>.
As the body of a function instead of a :ref:pass statement <tut-pass>.
In third-party libraries, such as Numpy's slicing and striding <https://numpy.org/doc/stable/user/basics.indexing.html#slicing-and-striding>_.

Python also uses three dots in ways that are not Ellipsis objects, for instance:

Doctest's :const:ELLIPSIS <doctest.ELLIPSIS>, as a pattern for missing content.
The default Python prompt of the :term:interactive shell when partial input is incomplete.

Lastly, the Python documentation often uses three dots in conventional English usage to mean omitted content, even in code examples that also use them as the Ellipsis.

.. _bltin-notimplemented-object:

The NotImplemented Object

This object is returned from comparisons and binary operations when they are asked to operate on types they don't support. See :ref:comparisons for more information. There is exactly one :data:NotImplemented object. :code:type(NotImplemented)() produces the singleton instance.

It is written as :code:NotImplemented.

.. _typesinternal:

Internal Objects

See :ref:types for this information. It describes :ref:stack frame objects <frame-objects>, :ref:traceback objects <traceback-objects>, and slice objects.

.. _specialattrs:

Special Attributes

The implementation adds a few special read-only attributes to several object types, where they are relevant. Some of these are not reported by the :func:dir built-in function.

.. attribute:: definition.name

The name of the class, function, method, descriptor, or generator instance.

.. attribute:: definition.qualname

The :term:qualified name of the class, function, method, descriptor, or generator instance.

.. versionadded:: 3.3

.. attribute:: definition.module

The name of the module in which a class or function was defined.

.. attribute:: definition.doc

The documentation string of a class or function, or None if undefined.

.. attribute:: definition.type_params

The :ref:type parameters <type-params> of generic classes, functions, and :ref:type aliases <type-aliases>. For classes and functions that are not generic, this will be an empty tuple.

.. versionadded:: 3.12

.. _int_max_str_digits:

Integer string conversion length limitation

CPython has a global limit for converting between :class:int and :class:str to mitigate denial of service attacks. This limit only applies to decimal or other non-power-of-two number bases. Hexadecimal, octal, and binary conversions are unlimited. The limit can be configured.

The :class:int type in CPython is an arbitrary length number stored in binary form (commonly known as a "bignum"). There exists no algorithm that can convert a string to a binary integer or a binary integer to a string in linear time, unless the base is a power of 2. Even the best known algorithms for base 10 have sub-quadratic complexity. Converting a large value such as int('1' * 500_000) can take over a second on a fast CPU.

Limiting conversion size offers a practical way to avoid :cve:2020-10735.

The limit is applied to the number of digit characters in the input or output string when a non-linear conversion algorithm would be involved. Underscores and the sign are not counted towards the limit.

When an operation would exceed the limit, a :exc:ValueError is raised:

.. doctest::

import sys sys.set_int_max_str_digits(4300) # Illustrative, this is the default. _ = int('2' * 5432) Traceback (most recent call last): ... ValueError: Exceeds the limit (4300 digits) for integer string conversion: value has 5432 digits; use sys.set_int_max_str_digits() to increase the limit i = int('2' * 4300) len(str(i)) 4300 i_squared = ii len(str(i_squared)) Traceback (most recent call last): ... ValueError: Exceeds the limit (4300 digits) for integer string conversion; use sys.set_int_max_str_digits() to increase the limit len(hex(i_squared)) 7144 assert int(hex(i_squared), base=16) == ii # Hexadecimal is unlimited.

The default limit is 4300 digits as provided in :data:sys.int_info.default_max_str_digits <sys.int_info>. The lowest limit that can be configured is 640 digits as provided in :data:sys.int_info.str_digits_check_threshold <sys.int_info>.

Verification:

.. doctest::

import sys assert sys.int_info.default_max_str_digits == 4300, sys.int_info assert sys.int_info.str_digits_check_threshold == 640, sys.int_info msg = int('578966293710682886880994035146873798396722250538762761564' ... '9252925514383915483333812743580549779436104706260696366600' ... '571186405732').to_bytes(53, 'big') ...

.. versionadded:: 3.11

Affected APIs

The limitation only applies to potentially slow conversions between :class:int and :class:str or :class:bytes:

int(string) with default base 10.
int(string, base) for all bases that are not a power of 2.
str(integer).
repr(integer).
any other string conversion to base 10, for example f"{integer}", "{}".format(integer), or b"%d" % integer.

The limitations do not apply to functions with a linear algorithm:

int(string, base) with base 2, 4, 8, 16, or 32.
:func:int.from_bytes and :func:int.to_bytes.
:func:hex, :func:oct, :func:bin.
:ref:formatspec for hex, octal, and binary numbers.
:class:str to :class:float.
:class:str to :class:decimal.Decimal.

Configuring the limit

Before Python starts up you can use an environment variable or an interpreter command line flag to configure the limit:

:envvar:PYTHONINTMAXSTRDIGITS, e.g. PYTHONINTMAXSTRDIGITS=640 python3 to set the limit to 640 or PYTHONINTMAXSTRDIGITS=0 python3 to disable the limitation.
:option:-X int_max_str_digits <-X>, e.g. python3 -X int_max_str_digits=640
:data:sys.flags.int_max_str_digits contains the value of :envvar:PYTHONINTMAXSTRDIGITS or :option:-X int_max_str_digits <-X>. If both the env var and the -X option are set, the -X option takes precedence. A value of -1 indicates that both were unset, thus a value of :data:sys.int_info.default_max_str_digits was used during initialization.

From code, you can inspect the current limit and set a new one using these :mod:sys APIs:

:func:sys.get_int_max_str_digits and :func:sys.set_int_max_str_digits are a getter and setter for the interpreter-wide limit. Subinterpreters have their own limit.

Information about the default and minimum can be found in :data:sys.int_info:

:data:sys.int_info.default_max_str_digits <sys.int_info> is the compiled-in default limit.
:data:sys.int_info.str_digits_check_threshold <sys.int_info> is the lowest accepted value for the limit (other than 0 which disables it).

.. versionadded:: 3.11

.. caution::

Setting a low limit can lead to problems. While rare, code exists that contains integer constants in decimal in their source that exceed the minimum threshold. A consequence of setting the limit is that Python source code containing decimal integer literals longer than the limit will encounter an error during parsing, usually at startup time or import time or even at installation time - anytime an up to date .pyc does not already exist for the code. A workaround for source that contains such large constants is to convert them to 0x hexadecimal form as it has no limit.

Test your application thoroughly if you use a low limit. Ensure your tests run with the limit set early via the environment or flag so that it applies during startup and even during any installation step that may invoke Python to precompile .py sources to .pyc files.

Recommended configuration

The default :data:sys.int_info.default_max_str_digits is expected to be reasonable for most applications. If your application requires a different limit, set it from your main entry point using Python version agnostic code as these APIs were added in security patch releases in versions before 3.12.

Example::

import sys if hasattr(sys, "set_int_max_str_digits"): ... upper_bound = 68000 ... lower_bound = 4004 ... current_limit = sys.get_int_max_str_digits() ... if current_limit == 0 or current_limit > upper_bound: ... sys.set_int_max_str_digits(upper_bound) ... elif current_limit < lower_bound: ... sys.set_int_max_str_digits(lower_bound)

If you need to disable it entirely, set it to 0.

.. rubric:: Footnotes

.. [1] Additional information on these special methods may be found in the Python Reference Manual (:ref:customization).

.. [2] As a consequence, the list [1, 2] is considered equal to [1.0, 2.0], and similarly for tuples.

.. [3] They must have since the parser can't tell the type of the operands.

.. [4] Cased characters are those with general category property being one of "Lu" (Letter, uppercase), "Ll" (Letter, lowercase), or "Lt" (Letter, titlecase).

.. [5] To format only a tuple you should therefore provide a singleton tuple whose only element is the tuple to be formatted.

Built-in Types

Truth Value Testing

Boolean Operations --- :keyword:!and, :keyword:!or, :keyword:!not

Comparisons

Numeric Types --- :class:int, :class:float, :class:complex

Bitwise Operations on Integer Types

Additional Methods on Integer Types

Additional Methods on Float

Additional Methods on Complex

Hashing of numeric types

Boolean Type - :class:bool

Iterator Types

Generator Types

Sequence Types --- :class:list, :class:tuple, :class:range

Common Sequence Operations

Immutable Sequence Types

Mutable Sequence Types

Lists

Tuples

Ranges

Text and Binary Sequence Type Methods Summary

Text Sequence Type --- :class:str

String Methods

Formatted String Literals (f-strings)

Template String Literals (t-strings)

printf-style String Formatting

Binary Sequence Types --- :class:bytes, :class:bytearray, :class:memoryview

Bytes Objects

Bytearray Objects

Bytes and Bytearray Operations

printf-style Bytes Formatting

Memory Views

Set Types --- :class:set, :class:frozenset

Mapping types --- :class:!dict, :class:!frozendict

Dictionary view objects

iteration

keys and values are iterated over in the same order (insertion order)

view objects are dynamic and reflect dict changes

set operations

get back a read-only proxy for the original dictionary

Frozen dictionaries

Context Manager Types

Type Annotation Types --- :ref:Generic Alias <types-genericalias>, :ref:Union <types-union>

Generic Alias Type

Union Type

Other Built-in Types

Modules

Classes and Class Instances

Functions

Methods

Code Objects

Type Objects

The Null Object

The Ellipsis Object

The NotImplemented Object

Internal Objects

Special Attributes

Integer string conversion length limitation

Affected APIs

Configuring the limit

Recommended configuration

Boolean Operations --- :keyword:`!and`, :keyword:`!or`, :keyword:`!not`

Numeric Types --- :class:`int`, :class:`float`, :class:`complex`

Boolean Type - :class:`bool`

Sequence Types --- :class:`list`, :class:`tuple`, :class:`range`

Text Sequence Type --- :class:`str`

`printf`-style String Formatting

Binary Sequence Types --- :class:`bytes`, :class:`bytearray`, :class:`memoryview`

`printf`-style Bytes Formatting

Set Types --- :class:`set`, :class:`frozenset`

Mapping types --- :class:`!dict`, :class:`!frozendict`

Type Annotation Types --- :ref:`Generic Alias <types-genericalias>`, :ref:`Union <types-union>`