:mod:`inspect` --- Inspect live objects

.. module:: inspect :synopsis: Extract information and source code from live objects.

.. moduleauthor:: Ka-Ping Yee [email protected] .. sectionauthor:: Ka-Ping Yee [email protected]

Source code: :source:Lib/inspect.py

The :mod:inspect module provides several useful functions to help get information about live objects such as modules, classes, methods, functions, tracebacks, frame objects, and code objects. For example, it can help you examine the contents of a class, retrieve the source code of a method, extract and format the argument list for a function, or get all the information you need to display a detailed traceback.

There are four main kinds of services provided by this module: type checking, getting source code, inspecting classes and functions, and examining the interpreter stack.

.. _inspect-types:

Types and members

The :func:getmembers function retrieves the members of an object such as a class or module. The functions whose names begin with "is" are mainly provided as convenient choices for the second argument to :func:getmembers. They also help you determine when you can expect to find the following special attributes:

.. this function name is too big to fit in the ascii-art table below .. |coroutine-origin-link| replace:: :func:sys.set_coroutine_origin_tracking_depth

.. versionchanged:: 3.5

Add __qualname__ and gi_yieldfrom attributes to generators.

The __name__ attribute of generators is now set from the function name, instead of the code name, and it can now be modified.

.. versionchanged:: 3.7

Add cr_origin attribute to coroutines.

.. function:: getmembers(object[, predicate])

Return all the members of an object in a list of (name, value) pairs sorted by name. If the optional predicate argument is supplied, only members for which the predicate returns a true value are included.

.. note::

  :func:`getmembers` will only return class attributes defined in the
  metaclass when the argument is a class and those attributes have been
  listed in the metaclass' custom :meth:`__dir__`.

.. function:: getmodulename(path)

Return the name of the module named by the file path, without including the names of enclosing packages. The file extension is checked against all of the entries in :func:importlib.machinery.all_suffixes. If it matches, the final path component is returned with the extension removed. Otherwise, None is returned.

Note that this function only returns a meaningful name for actual Python modules - paths that potentially refer to Python packages will still return None.

.. versionchanged:: 3.3 The function is based directly on :mod:importlib.

.. function:: ismodule(object)

Return true if the object is a module.

.. function:: isclass(object)

Return true if the object is a class, whether built-in or created in Python code.

.. function:: ismethod(object)

Return true if the object is a bound method written in Python.

.. function:: isfunction(object)

Return true if the object is a Python function, which includes functions created by a :term:lambda expression.

.. function:: isgeneratorfunction(object)

Return true if the object is a Python generator function.

.. function:: isgenerator(object)

Return true if the object is a generator.

.. function:: iscoroutinefunction(object)

Return true if the object is a :term:coroutine function (a function defined with an :keyword:async def syntax).

.. versionadded:: 3.5

.. function:: iscoroutine(object)

Return true if the object is a :term:coroutine created by an :keyword:async def function.

.. versionadded:: 3.5

.. function:: isawaitable(object)

Return true if the object can be used in :keyword:await expression.

Can also be used to distinguish generator-based coroutines from regular generators::

  def gen():
      yield
  @types.coroutine
  def gen_coro():
      yield

  assert not isawaitable(gen())
  assert isawaitable(gen_coro())

.. versionadded:: 3.5

.. function:: isasyncgenfunction(object)

Return true if the object is an :term:asynchronous generator function, for example::

>>> async def agen():
...     yield 1
...
>>> inspect.isasyncgenfunction(agen)
True

.. versionadded:: 3.6

.. function:: isasyncgen(object)

Return true if the object is an :term:asynchronous generator iterator created by an :term:asynchronous generator function.

.. versionadded:: 3.6

.. function:: istraceback(object)

Return true if the object is a traceback.

.. function:: isframe(object)

Return true if the object is a frame.

.. function:: iscode(object)

Return true if the object is a code.

.. function:: isbuiltin(object)

Return true if the object is a built-in function or a bound built-in method.

.. function:: isroutine(object)

Return true if the object is a user-defined or built-in function or method.

.. function:: isabstract(object)

Return true if the object is an abstract base class.

.. function:: ismethoddescriptor(object)

Return true if the object is a method descriptor, but not if :func:ismethod, :func:isclass, :func:isfunction or :func:isbuiltin are true.

This, for example, is true of int.__add__. An object passing this test has a :meth:~object.__get__ method but not a :meth:~object.__set__ method, but beyond that the set of attributes varies. A :attr:~definition.__name__ attribute is usually sensible, and :attr:__doc__ often is.

Methods implemented via descriptors that also pass one of the other tests return false from the :func:ismethoddescriptor test, simply because the other tests promise more -- you can, e.g., count on having the :attr:__func__ attribute (etc) when an object passes :func:ismethod.

.. function:: isdatadescriptor(object)

Return true if the object is a data descriptor.

Data descriptors have both a :attr:~object.__get__ and a :attr:~object.__set__ method. Examples are properties (defined in Python), getsets, and members. The latter two are defined in C and there are more specific tests available for those types, which is robust across Python implementations. Typically, data descriptors will also have :attr:~definition.__name__ and :attr:__doc__ attributes (properties, getsets, and members have both of these attributes), but this is not guaranteed.

.. function:: isgetsetdescriptor(object)

Return true if the object is a getset descriptor.

.. impl-detail::

  getsets are attributes defined in extension modules via
  :c:type:`PyGetSetDef` structures.  For Python implementations without such
  types, this method will always return ``False``.

.. function:: ismemberdescriptor(object)

Return true if the object is a member descriptor.

.. impl-detail::

  Member descriptors are attributes defined in extension modules via
  :c:type:`PyMemberDef` structures.  For Python implementations without such
  types, this method will always return ``False``.

.. _inspect-source:

Retrieving source code

.. function:: getdoc(object)

Get the documentation string for an object, cleaned up with :func:cleandoc. If the documentation string for an object is not provided and the object is a class, a method, a property or a descriptor, retrieve the documentation string from the inheritance hierarchy.

.. versionchanged:: 3.5 Documentation strings are now inherited if not overridden.

.. function:: getcomments(object)

Return in a single string any lines of comments immediately preceding the object's source code (for a class, function, or method), or at the top of the Python source file (if the object is a module). If the object's source code is unavailable, return None. This could happen if the object has been defined in C or the interactive shell.

.. function:: getfile(object)

Return the name of the (text or binary) file in which an object was defined. This will fail with a :exc:TypeError if the object is a built-in module, class, or function.

.. function:: getmodule(object)

Try to guess which module an object was defined in.

.. function:: getsourcefile(object)

Return the name of the Python source file in which an object was defined. This will fail with a :exc:TypeError if the object is a built-in module, class, or function.

.. function:: getsourcelines(object)

Return a list of source lines and starting line number for an object. The argument may be a module, class, method, function, traceback, frame, or code object. The source code is returned as a list of the lines corresponding to the object and the line number indicates where in the original source file the first line of code was found. An :exc:OSError is raised if the source code cannot be retrieved.

.. versionchanged:: 3.3 :exc:OSError is raised instead of :exc:IOError, now an alias of the former.

.. function:: getsource(object)

Return the text of the source code for an object. The argument may be a module, class, method, function, traceback, frame, or code object. The source code is returned as a single string. An :exc:OSError is raised if the source code cannot be retrieved.

.. versionchanged:: 3.3 :exc:OSError is raised instead of :exc:IOError, now an alias of the former.

.. function:: cleandoc(doc)

Clean up indentation from docstrings that are indented to line up with blocks of code.

All leading whitespace is removed from the first line. Any leading whitespace that can be uniformly removed from the second line onwards is removed. Empty lines at the beginning and end are subsequently removed. Also, all tabs are expanded to spaces.

.. _inspect-signature-object:

Introspecting callables with the Signature object

.. versionadded:: 3.3

The Signature object represents the call signature of a callable object and its return annotation. To retrieve a Signature object, use the :func:signature function.

.. function:: signature(callable, *, follow_wrapped=True)

Return a :class:Signature object for the given callable::

  >>> from inspect import signature
  >>> def foo(a, *, b:int, **kwargs):
  ...     pass

  >>> sig = signature(foo)

  >>> str(sig)
  '(a, *, b:int, **kwargs)'

  >>> str(sig.parameters['b'])
  'b:int'

  >>> sig.parameters['b'].annotation
  <class 'int'>

Accepts a wide range of Python callables, from plain functions and classes to :func:functools.partial objects.

Raises :exc:ValueError if no signature can be provided, and :exc:TypeError if that type of object is not supported.

A slash(/) in the signature of a function denotes that the parameters prior to it are positional-only. For more info, see :ref:the FAQ entry on positional-only parameters <faq-positional-only-arguments>.

.. versionadded:: 3.5 follow_wrapped parameter. Pass False to get a signature of callable specifically (callable.__wrapped__ will not be used to unwrap decorated callables.)

.. note::

  Some callables may not be introspectable in certain implementations of
  Python.  For example, in CPython, some built-in functions defined in
  C provide no metadata about their arguments.

.. class:: Signature(parameters=None, *, return_annotation=Signature.empty)

A Signature object represents the call signature of a function and its return annotation. For each parameter accepted by the function it stores a :class:Parameter object in its :attr:parameters collection.

The optional parameters argument is a sequence of :class:Parameter objects, which is validated to check that there are no parameters with duplicate names, and that the parameters are in the right order, i.e. positional-only first, then positional-or-keyword, and that parameters with defaults follow parameters without defaults.

The optional return_annotation argument, can be an arbitrary Python object, is the "return" annotation of the callable.

Signature objects are immutable. Use :meth:Signature.replace to make a modified copy.

.. versionchanged:: 3.5 Signature objects are picklable and hashable.

.. attribute:: Signature.empty

  A special class-level marker to specify absence of a return annotation.

.. attribute:: Signature.parameters

  An ordered mapping of parameters' names to the corresponding
  :class:`Parameter` objects.  Parameters appear in strict definition
  order, including keyword-only parameters.

  .. versionchanged:: 3.7
     Python only explicitly guaranteed that it preserved the declaration
     order of keyword-only parameters as of version 3.7, although in practice
     this order had always been preserved in Python 3.

.. attribute:: Signature.return_annotation

  The "return" annotation for the callable.  If the callable has no "return"
  annotation, this attribute is set to :attr:`Signature.empty`.

.. method:: Signature.bind(*args, **kwargs)

  Create a mapping from positional and keyword arguments to parameters.
  Returns :class:`BoundArguments` if ``*args`` and ``**kwargs`` match the
  signature, or raises a :exc:`TypeError`.

.. method:: Signature.bind_partial(*args, **kwargs)

  Works the same way as :meth:`Signature.bind`, but allows the omission of
  some required arguments (mimics :func:`functools.partial` behavior.)
  Returns :class:`BoundArguments`, or raises a :exc:`TypeError` if the
  passed arguments do not match the signature.

.. method:: Signature.replace(*[, parameters][, return_annotation])

  Create a new Signature instance based on the instance replace was invoked
  on.  It is possible to pass different ``parameters`` and/or
  ``return_annotation`` to override the corresponding properties of the base
  signature.  To remove return_annotation from the copied Signature, pass in
  :attr:`Signature.empty`.

  ::

     >>> def test(a, b):
     ...     pass
     >>> sig = signature(test)
     >>> new_sig = sig.replace(return_annotation="new return anno")
     >>> str(new_sig)
     "(a, b) -> 'new return anno'"

.. classmethod:: Signature.from_callable(obj, *, follow_wrapped=True)

   Return a :class:`Signature` (or its subclass) object for a given callable
   ``obj``.  Pass ``follow_wrapped=False`` to get a signature of ``obj``
   without unwrapping its ``__wrapped__`` chain.

   This method simplifies subclassing of :class:`Signature`::

     class MySignature(Signature):
         pass
     sig = MySignature.from_callable(min)
     assert isinstance(sig, MySignature)

   .. versionadded:: 3.5

.. class:: Parameter(name, kind, *, default=Parameter.empty, annotation=Parameter.empty)

Parameter objects are immutable. Instead of modifying a Parameter object, you can use :meth:Parameter.replace to create a modified copy.

.. versionchanged:: 3.5 Parameter objects are picklable and hashable.

.. attribute:: Parameter.empty

  A special class-level marker to specify absence of default values and
  annotations.

.. attribute:: Parameter.name

  The name of the parameter as a string.  The name must be a valid
  Python identifier.

  .. impl-detail::

     CPython generates implicit parameter names of the form ``.0`` on the
     code objects used to implement comprehensions and generator
     expressions.

     .. versionchanged:: 3.6
        These parameter names are exposed by this module as names like
        ``implicit0``.

.. attribute:: Parameter.default

  The default value for the parameter.  If the parameter has no default
  value, this attribute is set to :attr:`Parameter.empty`.

.. attribute:: Parameter.annotation

  The annotation for the parameter.  If the parameter has no annotation,
  this attribute is set to :attr:`Parameter.empty`.

.. attribute:: Parameter.kind

  Describes how argument values are bound to the parameter.  Possible values
  (accessible via :class:`Parameter`, like ``Parameter.KEYWORD_ONLY``):

  .. tabularcolumns:: |l|L|

  +------------------------+----------------------------------------------+
  |    Name                | Meaning                                      |
  +========================+==============================================+
  | *POSITIONAL_ONLY*      | Value must be supplied as a positional       |
  |                        | argument.                                    |
  |                        |                                              |
  |                        | Python has no explicit syntax for defining   |
  |                        | positional-only parameters, but many built-in|
  |                        | and extension module functions (especially   |
  |                        | those that accept only one or two parameters)|
  |                        | accept them.                                 |
  +------------------------+----------------------------------------------+
  | *POSITIONAL_OR_KEYWORD*| Value may be supplied as either a keyword or |
  |                        | positional argument (this is the standard    |
  |                        | binding behaviour for functions implemented  |
  |                        | in Python.)                                  |
  +------------------------+----------------------------------------------+
  | *VAR_POSITIONAL*       | A tuple of positional arguments that aren't  |
  |                        | bound to any other parameter. This           |
  |                        | corresponds to a ``*args`` parameter in a    |
  |                        | Python function definition.                  |
  +------------------------+----------------------------------------------+
  | *KEYWORD_ONLY*         | Value must be supplied as a keyword argument.|
  |                        | Keyword only parameters are those which      |
  |                        | appear after a ``*`` or ``*args`` entry in a |
  |                        | Python function definition.                  |
  +------------------------+----------------------------------------------+
  | *VAR_KEYWORD*          | A dict of keyword arguments that aren't bound|
  |                        | to any other parameter. This corresponds to a|
  |                        | ``**kwargs`` parameter in a Python function  |
  |                        | definition.                                  |
  +------------------------+----------------------------------------------+

  Example: print all keyword-only arguments without default values::

     >>> def foo(a, b, *, c, d=10):
     ...     pass

     >>> sig = signature(foo)
     >>> for param in sig.parameters.values():
     ...     if (param.kind == param.KEYWORD_ONLY and
     ...                        param.default is param.empty):
     ...         print('Parameter:', param)
     Parameter: c

.. method:: Parameter.replace(*[, name][, kind][, default][, annotation])

  Create a new Parameter instance based on the instance replaced was invoked
  on.  To override a :class:`Parameter` attribute, pass the corresponding
  argument.  To remove a default value or/and an annotation from a
  Parameter, pass :attr:`Parameter.empty`.

  ::

     >>> from inspect import Parameter
     >>> param = Parameter('foo', Parameter.KEYWORD_ONLY, default=42)
     >>> str(param)
     'foo=42'

     >>> str(param.replace()) # Will create a shallow copy of 'param'
     'foo=42'

     >>> str(param.replace(default=Parameter.empty, annotation='spam'))
     "foo:'spam'"

.. versionchanged:: 3.4
    In Python 3.3 Parameter objects were allowed to have ``name`` set
    to ``None`` if their ``kind`` was set to ``POSITIONAL_ONLY``.
    This is no longer permitted.

.. class:: BoundArguments

Result of a :meth:Signature.bind or :meth:Signature.bind_partial call. Holds the mapping of arguments to the function's parameters.

.. attribute:: BoundArguments.arguments

  An ordered, mutable mapping (:class:`collections.OrderedDict`) of
  parameters' names to arguments' values.  Contains only explicitly bound
  arguments.  Changes in :attr:`arguments` will reflect in :attr:`args` and
  :attr:`kwargs`.

  Should be used in conjunction with :attr:`Signature.parameters` for any
  argument processing purposes.

  .. note::

     Arguments for which :meth:`Signature.bind` or
     :meth:`Signature.bind_partial` relied on a default value are skipped.
     However, if needed, use :meth:`BoundArguments.apply_defaults` to add
     them.

.. attribute:: BoundArguments.args

  A tuple of positional arguments values.  Dynamically computed from the
  :attr:`arguments` attribute.

.. attribute:: BoundArguments.kwargs

  A dict of keyword arguments values.  Dynamically computed from the
  :attr:`arguments` attribute.

.. attribute:: BoundArguments.signature

  A reference to the parent :class:`Signature` object.

.. method:: BoundArguments.apply_defaults()

  Set default values for missing arguments.

  For variable-positional arguments (``*args``) the default is an
  empty tuple.

  For variable-keyword arguments (``**kwargs``) the default is an
  empty dict.

  ::

    >>> def foo(a, b='ham', *args): pass
    >>> ba = inspect.signature(foo).bind('spam')
    >>> ba.apply_defaults()
    >>> ba.arguments
    OrderedDict([('a', 'spam'), ('b', 'ham'), ('args', ())])

  .. versionadded:: 3.5

The :attr:args and :attr:kwargs properties can be used to invoke functions::

  def test(a, *, b):
      ...

  sig = signature(test)
  ba = sig.bind(10, b=20)
  test(*ba.args, **ba.kwargs)

.. seealso::

:pep:362 - Function Signature Object. The detailed specification, implementation details and examples.

.. _inspect-classes-functions:

Classes and functions

.. function:: getclasstree(classes, unique=False)

Arrange the given list of classes into a hierarchy of nested lists. Where a nested list appears, it contains classes derived from the class whose entry immediately precedes the list. Each entry is a 2-tuple containing a class and a tuple of its base classes. If the unique argument is true, exactly one entry appears in the returned structure for each class in the given list. Otherwise, classes using multiple inheritance and their descendants will appear multiple times.

.. function:: getargspec(func)

Get the names and default values of a Python function's parameters. A :term:named tuple ArgSpec(args, varargs, keywords, defaults) is returned. args is a list of the parameter names. varargs and keywords are the names of the * and ** parameters or None. defaults is a tuple of default argument values or None if there are no default arguments; if this tuple has n elements, they correspond to the last n elements listed in args.

.. deprecated:: 3.0 Use :func:getfullargspec for an updated API that is usually a drop-in replacement, but also correctly handles function annotations and keyword-only parameters.

  Alternatively, use :func:`signature` and
  :ref:`Signature Object <inspect-signature-object>`, which provide a
  more structured introspection API for callables.

.. function:: getfullargspec(func)

Get the names and default values of a Python function's parameters. A :term:named tuple is returned:

FullArgSpec(args, varargs, varkw, defaults, kwonlyargs, kwonlydefaults, annotations)

args is a list of the positional parameter names. varargs is the name of the * parameter or None if arbitrary positional arguments are not accepted. varkw is the name of the ** parameter or None if arbitrary keyword arguments are not accepted. defaults is an n-tuple of default argument values corresponding to the last n positional parameters, or None if there are no such defaults defined. kwonlyargs is a list of keyword-only parameter names in declaration order. kwonlydefaults is a dictionary mapping parameter names from kwonlyargs to the default values used if no argument is supplied. annotations is a dictionary mapping parameter names to annotations. The special key "return" is used to report the function return value annotation (if any).

Note that :func:signature and :ref:Signature Object <inspect-signature-object> provide the recommended API for callable introspection, and support additional behaviours (like positional-only arguments) that are sometimes encountered in extension module APIs. This function is retained primarily for use in code that needs to maintain compatibility with the Python 2 inspect module API.

.. versionchanged:: 3.4 This function is now based on :func:signature, but still ignores __wrapped__ attributes and includes the already bound first parameter in the signature output for bound methods.

.. versionchanged:: 3.6 This method was previously documented as deprecated in favour of :func:signature in Python 3.5, but that decision has been reversed in order to restore a clearly supported standard interface for single-source Python 2/3 code migrating away from the legacy :func:getargspec API.

.. versionchanged:: 3.7 Python only explicitly guaranteed that it preserved the declaration order of keyword-only parameters as of version 3.7, although in practice this order had always been preserved in Python 3.

.. function:: getargvalues(frame)

Get information about arguments passed into a particular frame. A :term:named tuple ArgInfo(args, varargs, keywords, locals) is returned. args is a list of the argument names. varargs and keywords are the names of the * and ** arguments or None. locals is the locals dictionary of the given frame.

.. note:: This function was inadvertently marked as deprecated in Python 3.5.

.. function:: formatargspec(args[, varargs, varkw, defaults, kwonlyargs, kwonlydefaults, annotations[, formatarg, formatvarargs, formatvarkw, formatvalue, formatreturns, formatannotations]])

Format a pretty argument spec from the values returned by :func:getfullargspec.

The first seven arguments are (args, varargs, varkw, defaults, kwonlyargs, kwonlydefaults, annotations).

The other six arguments are functions that are called to turn argument names, * argument name, ** argument name, default values, return annotation and individual annotations into strings, respectively.

For example:

from inspect import formatargspec, getfullargspec def f(a: int, b: float): ... pass ... formatargspec(*getfullargspec(f)) '(a: int, b: float)'

.. deprecated:: 3.5 Use :func:signature and :ref:Signature Object <inspect-signature-object>, which provide a better introspecting API for callables.

.. function:: formatargvalues(args[, varargs, varkw, locals, formatarg, formatvarargs, formatvarkw, formatvalue])

Format a pretty argument spec from the four values returned by :func:getargvalues. The format* arguments are the corresponding optional formatting functions that are called to turn names and values into strings.

.. note:: This function was inadvertently marked as deprecated in Python 3.5.

.. function:: getmro(cls)

Return a tuple of class cls's base classes, including cls, in method resolution order. No class appears more than once in this tuple. Note that the method resolution order depends on cls's type. Unless a very peculiar user-defined metatype is in use, cls will be the first element of the tuple.

.. function:: getcallargs(func, *args, **kwds)

Bind the args and kwds to the argument names of the Python function or method func, as if it was called with them. For bound methods, bind also the first argument (typically named self) to the associated instance. A dict is returned, mapping the argument names (including the names of the * and ** arguments, if any) to their values from args and kwds. In case of invoking func incorrectly, i.e. whenever func(*args, **kwds) would raise an exception because of incompatible signature, an exception of the same type and the same or similar message is raised. For example::

>>> from inspect import getcallargs
>>> def f(a, b=1, *pos, **named):
...     pass
>>> getcallargs(f, 1, 2, 3) == {'a': 1, 'named': {}, 'b': 2, 'pos': (3,)}
True
>>> getcallargs(f, a=2, x=4) == {'a': 2, 'named': {'x': 4}, 'b': 1, 'pos': ()}
True
>>> getcallargs(f)
Traceback (most recent call last):
...
TypeError: f() missing 1 required positional argument: 'a'

.. versionadded:: 3.2

.. deprecated:: 3.5 Use :meth:Signature.bind and :meth:Signature.bind_partial instead.

.. function:: getclosurevars(func)

Get the mapping of external name references in a Python function or method func to their current values. A :term:named tuple ClosureVars(nonlocals, globals, builtins, unbound) is returned. nonlocals maps referenced names to lexical closure variables, globals to the function's module globals and builtins to the builtins visible from the function body. unbound is the set of names referenced in the function that could not be resolved at all given the current module globals and builtins.

:exc:TypeError is raised if func is not a Python function or method.

.. versionadded:: 3.3

.. function:: unwrap(func, *, stop=None)

Get the object wrapped by func. It follows the chain of :attr:__wrapped__ attributes returning the last object in the chain.

stop is an optional callback accepting an object in the wrapper chain as its sole argument that allows the unwrapping to be terminated early if the callback returns a true value. If the callback never returns a true value, the last object in the chain is returned as usual. For example, :func:signature uses this to stop unwrapping if any object in the chain has a __signature__ attribute defined.

:exc:ValueError is raised if a cycle is encountered.

.. versionadded:: 3.4

.. _inspect-stack:

The interpreter stack

When the following functions return "frame records," each record is a :term:named tuple FrameInfo(frame, filename, lineno, function, code_context, index). The tuple contains the frame object, the filename, the line number of the current line, the function name, a list of lines of context from the source code, and the index of the current line within that list.

.. versionchanged:: 3.5 Return a named tuple instead of a tuple.

.. note::

Keeping references to frame objects, as found in the first element of the frame records these functions return, can cause your program to create reference cycles. Once a reference cycle has been created, the lifespan of all objects which can be accessed from the objects which form the cycle can become much longer even if Python's optional cycle detector is enabled. If such cycles must be created, it is important to ensure they are explicitly broken to avoid the delayed destruction of objects and increased memory consumption which occurs.

Though the cycle detector will catch these, destruction of the frames (and local variables) can be made deterministic by removing the cycle in a :keyword:finally clause. This is also important if the cycle detector was disabled when Python was compiled or using :func:gc.disable. For example::

  def handle_stackframe_without_leak():
      frame = inspect.currentframe()
      try:
          # do something with the frame
      finally:
          del frame

If you want to keep the frame around (for example to print a traceback later), you can also break reference cycles by using the :meth:frame.clear method.

The optional context argument supported by most of these functions specifies the number of lines of context to return, which are centered around the current line.

.. function:: getframeinfo(frame, context=1)

Get information about a frame or traceback object. A :term:named tuple Traceback(filename, lineno, function, code_context, index) is returned.

.. function:: getouterframes(frame, context=1)

Get a list of frame records for a frame and all outer frames. These frames represent the calls that lead to the creation of frame. The first entry in the returned list represents frame; the last entry represents the outermost call on frame's stack.

.. versionchanged:: 3.5 A list of :term:named tuples <named tuple> FrameInfo(frame, filename, lineno, function, code_context, index) is returned.

.. function:: getinnerframes(traceback, context=1)

Get a list of frame records for a traceback's frame and all inner frames. These frames represent calls made as a consequence of frame. The first entry in the list represents traceback; the last entry represents where the exception was raised.

.. versionchanged:: 3.5 A list of :term:named tuples <named tuple> FrameInfo(frame, filename, lineno, function, code_context, index) is returned.

.. function:: currentframe()

Return the frame object for the caller's stack frame.

.. impl-detail::

  This function relies on Python stack frame support in the interpreter,
  which isn't guaranteed to exist in all implementations of Python.  If
  running in an implementation without Python stack frame support this
  function returns ``None``.

.. function:: stack(context=1)

Return a list of frame records for the caller's stack. The first entry in the returned list represents the caller; the last entry represents the outermost call on the stack.

.. versionchanged:: 3.5 A list of :term:named tuples <named tuple> FrameInfo(frame, filename, lineno, function, code_context, index) is returned.

.. function:: trace(context=1)

Return a list of frame records for the stack between the current frame and the frame in which an exception currently being handled was raised in. The first entry in the list represents the caller; the last entry represents where the exception was raised.

.. versionchanged:: 3.5 A list of :term:named tuples <named tuple> FrameInfo(frame, filename, lineno, function, code_context, index) is returned.

Fetching attributes statically

Both :func:getattr and :func:hasattr can trigger code execution when fetching or checking for the existence of attributes. Descriptors, like properties, will be invoked and :meth:__getattr__ and :meth:__getattribute__ may be called.

For cases where you want passive introspection, like documentation tools, this can be inconvenient. :func:getattr_static has the same signature as :func:getattr but avoids executing code when it fetches attributes.

.. function:: getattr_static(obj, attr, default=None)

Retrieve attributes without triggering dynamic lookup via the descriptor protocol, :meth:__getattr__ or :meth:__getattribute__.

Note: this function may not be able to retrieve all attributes that getattr can fetch (like dynamically created attributes) and may find attributes that getattr can't (like descriptors that raise AttributeError). It can also return descriptors objects instead of instance members.

If the instance :attr:~object.__dict__ is shadowed by another member (for example a property) then this function will be unable to find instance members.

.. versionadded:: 3.2

:func:getattr_static does not resolve descriptors, for example slot descriptors or getset descriptors on objects implemented in C. The descriptor object is returned instead of the underlying attribute.

You can handle these with code like the following. Note that for arbitrary getset descriptors invoking these may trigger code execution::

example code for resolving the builtin descriptor types

class _foo: slots = ['foo']

slot_descriptor = type(_foo.foo) getset_descriptor = type(type(open(file)).name) wrapper_descriptor = type(str.dict['add']) descriptor_types = (slot_descriptor, getset_descriptor, wrapper_descriptor)

result = getattr_static(some_object, 'foo') if type(result) in descriptor_types: try: result = result.get() except AttributeError: # descriptors can raise AttributeError to # indicate there is no underlying value # in which case the descriptor itself will # have to do pass

Current State of Generators and Coroutines

When implementing coroutine schedulers and for other advanced uses of generators, it is useful to determine whether a generator is currently executing, is waiting to start or resume or execution, or has already terminated. :func:getgeneratorstate allows the current state of a generator to be determined easily.

.. function:: getgeneratorstate(generator)

Get current state of a generator-iterator.

Possible states are: * GEN_CREATED: Waiting to start execution. * GEN_RUNNING: Currently being executed by the interpreter. * GEN_SUSPENDED: Currently suspended at a yield expression. * GEN_CLOSED: Execution has completed.

.. versionadded:: 3.2

.. function:: getcoroutinestate(coroutine)

Get current state of a coroutine object. The function is intended to be used with coroutine objects created by :keyword:async def functions, but will accept any coroutine-like object that has cr_running and cr_frame attributes.

Possible states are: * CORO_CREATED: Waiting to start execution. * CORO_RUNNING: Currently being executed by the interpreter. * CORO_SUSPENDED: Currently suspended at an await expression. * CORO_CLOSED: Execution has completed.

.. versionadded:: 3.5

The current internal state of the generator can also be queried. This is mostly useful for testing purposes, to ensure that internal state is being updated as expected:

.. function:: getgeneratorlocals(generator)

Get the mapping of live local variables in generator to their current values. A dictionary is returned that maps from variable names to values. This is the equivalent of calling :func:locals in the body of the generator, and all the same caveats apply.

If generator is a :term:generator with no currently associated frame, then an empty dictionary is returned. :exc:TypeError is raised if generator is not a Python generator object.

.. impl-detail::

  This function relies on the generator exposing a Python stack frame
  for introspection, which isn't guaranteed to be the case in all
  implementations of Python. In such cases, this function will always
  return an empty dictionary.

.. versionadded:: 3.3

.. function:: getcoroutinelocals(coroutine)

This function is analogous to :func:~inspect.getgeneratorlocals, but works for coroutine objects created by :keyword:async def functions.

.. versionadded:: 3.5

.. _inspect-module-co-flags:

Code Objects Bit Flags

Python code objects have a co_flags attribute, which is a bitmap of the following flags:

.. data:: CO_OPTIMIZED

The code object is optimized, using fast locals.

.. data:: CO_NEWLOCALS

If set, a new dict will be created for the frame's f_locals when the code object is executed.

.. data:: CO_VARARGS

The code object has a variable positional parameter (*args-like).

.. data:: CO_VARKEYWORDS

The code object has a variable keyword parameter (**kwargs-like).

.. data:: CO_NESTED

The flag is set when the code object is a nested function.

.. data:: CO_GENERATOR

The flag is set when the code object is a generator function, i.e. a generator object is returned when the code object is executed.

.. data:: CO_NOFREE

The flag is set if there are no free or cell variables.

.. data:: CO_COROUTINE

The flag is set when the code object is a coroutine function. When the code object is executed it returns a coroutine object. See :pep:492 for more details.

.. versionadded:: 3.5

.. data:: CO_ITERABLE_COROUTINE

The flag is used to transform generators into generator-based coroutines. Generator objects with this flag can be used in await expression, and can yield from coroutine objects. See :pep:492 for more details.

.. versionadded:: 3.5

.. data:: CO_ASYNC_GENERATOR

The flag is set when the code object is an asynchronous generator function. When the code object is executed it returns an asynchronous generator object. See :pep:525 for more details.

.. versionadded:: 3.6

.. note:: The flags are specific to CPython, and may not be defined in other Python implementations. Furthermore, the flags are an implementation detail, and can be removed or deprecated in future Python releases. It's recommended to use public APIs from the :mod:inspect module for any introspection needs.

.. _inspect-module-cli:

Command Line Interface

The :mod:inspect module also provides a basic introspection capability from the command line.

.. program:: inspect

By default, accepts the name of a module and prints the source of that module. A class or function within the module can be printed instead by appended a colon and the qualified name of the target object.

.. cmdoption:: --details

Print information about the specified object rather than the source code

:mod:`inspect` --- Inspect live objects

:mod:inspect --- Inspect live objects

Types and members

Retrieving source code

Introspecting callables with the Signature object

Classes and functions

The interpreter stack

Fetching attributes statically

example code for resolving the builtin descriptor types

Current State of Generators and Coroutines

Code Objects Bit Flags

Command Line Interface

:mod:`inspect` --- Inspect live objects