kbe/src/lib/python/Doc/library/2to3.rst
.. _2to3-reference:
.. sectionauthor:: Benjamin Peterson [email protected]
2to3 is a Python program that reads Python 2.x source code and applies a series
of fixers to transform it into valid Python 3.x code. The standard library
contains a rich set of fixers that will handle almost all code. 2to3 supporting
library :mod:lib2to3 is, however, a flexible and generic library, so it is
possible to write your own fixers for 2to3. :mod:lib2to3 could also be
adapted to custom applications in which Python code needs to be edited
automatically.
.. _2to3-using:
2to3 will usually be installed with the Python interpreter as a script. It is
also located in the :file:Tools/scripts directory of the Python root.
2to3's basic arguments are a list of files or directories to transform. The directories are recursively traversed for Python sources.
Here is a sample Python 2.x source file, :file:example.py::
def greet(name): print "Hello, {0}!".format(name) print "What's your name?" name = raw_input() greet(name)
It can be converted to Python 3.x code via 2to3 on the command line:
.. code-block:: shell-session
$ 2to3 example.py
A diff against the original source file is printed. 2to3 can also write the
needed modifications right back to the source file. (A backup of the original
file is made unless :option:!-n is also given.) Writing the changes back is
enabled with the :option:!-w flag:
.. code-block:: shell-session
$ 2to3 -w example.py
After transformation, :file:example.py looks like this::
def greet(name): print("Hello, {0}!".format(name)) print("What's your name?") name = input() greet(name)
Comments and exact indentation are preserved throughout the translation process.
By default, 2to3 runs a set of :ref:predefined fixers <2to3-fixers>. The
:option:!-l flag lists all available fixers. An explicit set of fixers to run
can be given with :option:!-f. Likewise the :option:!-x explicitly disables a
fixer. The following example runs only the imports and has_key fixers:
.. code-block:: shell-session
$ 2to3 -f imports -f has_key example.py
This command runs every fixer except the apply fixer:
.. code-block:: shell-session
$ 2to3 -x apply example.py
Some fixers are explicit, meaning they aren't run by default and must be
listed on the command line to be run. Here, in addition to the default fixers,
the idioms fixer is run:
.. code-block:: shell-session
$ 2to3 -f all -f idioms example.py
Notice how passing all enables all default fixers.
Sometimes 2to3 will find a place in your source code that needs to be changed, but 2to3 cannot fix automatically. In this case, 2to3 will print a warning beneath the diff for a file. You should address the warning in order to have compliant 3.x code.
2to3 can also refactor doctests. To enable this mode, use the :option:!-d
flag. Note that only doctests will be refactored. This also doesn't require
the module to be valid Python. For example, doctest like examples in a reST
document could also be refactored with this option.
The :option:!-v option enables output of more information on the translation
process.
Since some print statements can be parsed as function calls or statements, 2to3
cannot always read files containing the print function. When 2to3 detects the
presence of the from __future__ import print_function compiler directive, it
modifies its internal grammar to interpret :func:print as a function. This
change can also be enabled manually with the :option:!-p flag. Use
:option:!-p to run fixers on code that already has had its print statements
converted.
The :option:!-o or :option:!--output-dir option allows specification of an
alternate directory for processed output files to be written to. The
:option:!-n flag is required when using this as backup files do not make sense
when not overwriting the input files.
.. versionadded:: 3.2.3
The :option:!-o option was added.
The :option:!-W or :option:!--write-unchanged-files flag tells 2to3 to always
write output files even if no changes were required to the file. This is most
useful with :option:!-o so that an entire Python source tree is copied with
translation from one directory to another.
This option implies the :option:!-w flag as it would not make sense otherwise.
.. versionadded:: 3.2.3
The :option:!-W flag was added.
The :option:!--add-suffix option specifies a string to append to all output
filenames. The :option:!-n flag is required when specifying this as backups
are not necessary when writing to different filenames. Example:
.. code-block:: shell-session
$ 2to3 -n -W --add-suffix=3 example.py
Will cause a converted file named example.py3 to be written.
.. versionadded:: 3.2.3
The :option:!--add-suffix option was added.
To translate an entire project from one directory tree to another use:
.. code-block:: shell-session
$ 2to3 --output-dir=python3-version/mycode -W -n python2-version/mycode
.. _2to3-fixers:
Each step of transforming code is encapsulated in a fixer. The command 2to3 -l lists them. As :ref:documented above <2to3-using>, each can be turned on
and off individually. They are described here in more detail.
.. 2to3fixer:: apply
Removes usage of :func:apply. For example apply(function, *args, **kwargs) is converted to function(*args, **kwargs).
.. 2to3fixer:: asserts
Replaces deprecated :mod:unittest method names with the correct ones.
================================ ==========================================
From To
================================ ==========================================
failUnlessEqual(a, b) :meth:assertEqual(a, b) <unittest.TestCase.assertEqual>
assertEquals(a, b) :meth:assertEqual(a, b) <unittest.TestCase.assertEqual>
failIfEqual(a, b) :meth:assertNotEqual(a, b) <unittest.TestCase.assertNotEqual>
assertNotEquals(a, b) :meth:assertNotEqual(a, b) <unittest.TestCase.assertNotEqual>
failUnless(a) :meth:assertTrue(a) <unittest.TestCase.assertTrue>
assert_(a) :meth:assertTrue(a) <unittest.TestCase.assertTrue>
failIf(a) :meth:assertFalse(a) <unittest.TestCase.assertFalse>
failUnlessRaises(exc, cal) :meth:assertRaises(exc, cal) <unittest.TestCase.assertRaises>
failUnlessAlmostEqual(a, b) :meth:assertAlmostEqual(a, b) <unittest.TestCase.assertAlmostEqual>
assertAlmostEquals(a, b) :meth:assertAlmostEqual(a, b) <unittest.TestCase.assertAlmostEqual>
failIfAlmostEqual(a, b) :meth:assertNotAlmostEqual(a, b) <unittest.TestCase.assertNotAlmostEqual>
assertNotAlmostEquals(a, b) :meth:assertNotAlmostEqual(a, b) <unittest.TestCase.assertNotAlmostEqual>
================================ ==========================================
.. 2to3fixer:: basestring
Converts :class:basestring to :class:str.
.. 2to3fixer:: buffer
Converts :class:buffer to :class:memoryview. This fixer is optional
because the :class:memoryview API is similar but not exactly the same as
that of :class:buffer.
.. 2to3fixer:: dict
Fixes dictionary iteration methods. :meth:dict.iteritems is converted to
:meth:dict.items, :meth:dict.iterkeys to :meth:dict.keys, and
:meth:dict.itervalues to :meth:dict.values. Similarly,
:meth:dict.viewitems, :meth:dict.viewkeys and :meth:dict.viewvalues are
converted respectively to :meth:dict.items, :meth:dict.keys and
:meth:dict.values. It also wraps existing usages of :meth:dict.items,
:meth:dict.keys, and :meth:dict.values in a call to :class:list.
.. 2to3fixer:: except
Converts except X, T to except X as T.
.. 2to3fixer:: exec
Converts the exec statement to the :func:exec function.
.. 2to3fixer:: execfile
Removes usage of :func:execfile. The argument to :func:execfile is
wrapped in calls to :func:open, :func:compile, and :func:exec.
.. 2to3fixer:: exitfunc
Changes assignment of :attr:sys.exitfunc to use of the :mod:atexit
module.
.. 2to3fixer:: filter
Wraps :func:filter usage in a :class:list call.
.. 2to3fixer:: funcattrs
Fixes function attributes that have been renamed. For example,
my_function.func_closure is converted to my_function.__closure__.
.. 2to3fixer:: future
Removes from __future__ import new_feature statements.
.. 2to3fixer:: getcwdu
Renames :func:os.getcwdu to :func:os.getcwd.
.. 2to3fixer:: has_key
Changes dict.has_key(key) to key in dict.
.. 2to3fixer:: idioms
This optional fixer performs several transformations that make Python code
more idiomatic. Type comparisons like type(x) is SomeClass and
type(x) == SomeClass are converted to isinstance(x, SomeClass).
while 1 becomes while True. This fixer also tries to make use of
:func:sorted in appropriate places. For example, this block ::
L = list(some_iterable)
L.sort()
is changed to ::
L = sorted(some_iterable)
.. 2to3fixer:: import
Detects sibling imports and converts them to relative imports.
.. 2to3fixer:: imports
Handles module renames in the standard library.
.. 2to3fixer:: imports2
Handles other modules renames in the standard library. It is separate from
the :2to3fixer:imports fixer only because of technical limitations.
.. 2to3fixer:: input
Converts input(prompt) to eval(input(prompt)).
.. 2to3fixer:: intern
Converts :func:intern to :func:sys.intern.
.. 2to3fixer:: isinstance
Fixes duplicate types in the second argument of :func:isinstance. For
example, isinstance(x, (int, int)) is converted to isinstance(x, int) and isinstance(x, (int, float, int)) is converted to
isinstance(x, (int, float)).
.. 2to3fixer:: itertools_imports
Removes imports of :func:itertools.ifilter, :func:itertools.izip, and
:func:itertools.imap. Imports of :func:itertools.ifilterfalse are also
changed to :func:itertools.filterfalse.
.. 2to3fixer:: itertools
Changes usage of :func:itertools.ifilter, :func:itertools.izip, and
:func:itertools.imap to their built-in equivalents.
:func:itertools.ifilterfalse is changed to :func:itertools.filterfalse.
.. 2to3fixer:: long
Renames :class:long to :class:int.
.. 2to3fixer:: map
Wraps :func:map in a :class:list call. It also changes map(None, x)
to list(x). Using from future_builtins import map disables this
fixer.
.. 2to3fixer:: metaclass
Converts the old metaclass syntax (__metaclass__ = Meta in the class
body) to the new (class X(metaclass=Meta)).
.. 2to3fixer:: methodattrs
Fixes old method attribute names. For example, meth.im_func is converted
to meth.__func__.
.. 2to3fixer:: ne
Converts the old not-equal syntax, <>, to !=.
.. 2to3fixer:: next
Converts the use of iterator's :meth:~iterator.next methods to the
:func:next function. It also renames :meth:next methods to
:meth:~iterator.__next__.
.. 2to3fixer:: nonzero
Renames :meth:__nonzero__ to :meth:~object.__bool__.
.. 2to3fixer:: numliterals
Converts octal literals into the new syntax.
.. 2to3fixer:: operator
Converts calls to various functions in the :mod:operator module to other,
but equivalent, function calls. When needed, the appropriate import
statements are added, e.g. import collections.abc. The following mapping
are made:
================================== =============================================
From To
================================== =============================================
operator.isCallable(obj) callable(obj)
operator.sequenceIncludes(obj) operator.contains(obj)
operator.isSequenceType(obj) isinstance(obj, collections.abc.Sequence)
operator.isMappingType(obj) isinstance(obj, collections.abc.Mapping)
operator.isNumberType(obj) isinstance(obj, numbers.Number)
operator.repeat(obj, n) operator.mul(obj, n)
operator.irepeat(obj, n) operator.imul(obj, n)
================================== =============================================
.. 2to3fixer:: paren
Add extra parenthesis where they are required in list comprehensions. For
example, [x for x in 1, 2] becomes [x for x in (1, 2)].
.. 2to3fixer:: print
Converts the print statement to the :func:print function.
.. 2to3fixer:: raise
Converts raise E, V to raise E(V), and raise E, V, T to raise E(V).with_traceback(T). If E is a tuple, the translation will be
incorrect because substituting tuples for exceptions has been removed in 3.0.
.. 2to3fixer:: raw_input
Converts :func:raw_input to :func:input.
.. 2to3fixer:: reduce
Handles the move of :func:reduce to :func:functools.reduce.
.. 2to3fixer:: reload
Converts :func:reload to :func:importlib.reload.
.. 2to3fixer:: renames
Changes :data:sys.maxint to :data:sys.maxsize.
.. 2to3fixer:: repr
Replaces backtick repr with the :func:repr function.
.. 2to3fixer:: set_literal
Replaces use of the :class:set constructor with set literals. This fixer
is optional.
.. 2to3fixer:: standarderror
Renames :exc:StandardError to :exc:Exception.
.. 2to3fixer:: sys_exc
Changes the deprecated :data:sys.exc_value, :data:sys.exc_type,
:data:sys.exc_traceback to use :func:sys.exc_info.
.. 2to3fixer:: throw
Fixes the API change in generator's :meth:throw method.
.. 2to3fixer:: tuple_params
Removes implicit tuple parameter unpacking. This fixer inserts temporary variables.
.. 2to3fixer:: types
Fixes code broken from the removal of some members in the :mod:types
module.
.. 2to3fixer:: unicode
Renames :class:unicode to :class:str.
.. 2to3fixer:: urllib
Handles the rename of :mod:urllib and :mod:urllib2 to the :mod:urllib
package.
.. 2to3fixer:: ws_comma
Removes excess whitespace from comma separated items. This fixer is optional.
.. 2to3fixer:: xrange
Renames :func:xrange to :func:range and wraps existing :func:range
calls with :class:list.
.. 2to3fixer:: xreadlines
Changes for x in file.xreadlines() to for x in file.
.. 2to3fixer:: zip
Wraps :func:zip usage in a :class:list call. This is disabled when
from future_builtins import zip appears.
lib2to3 - 2to3's library.. module:: lib2to3 :synopsis: the 2to3 library
.. moduleauthor:: Guido van Rossum .. moduleauthor:: Collin Winter .. moduleauthor:: Benjamin Peterson [email protected]
Source code: :source:Lib/lib2to3/
.. note::
The :mod:lib2to3 API should be considered unstable and may change
drastically in the future.
.. XXX What is the public interface anyway?