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

=======================================

.. module:: inspect

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

.. moduleauthor:: Ka-Ping Yee <ping@lfw.org>

.. sectionauthor:: Ka-Ping Yee <ping@lfw.org>

.. versionadded:: 2.1

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 sixteen 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:

+-----------+-----------------+---------------------------+-------+

| Type      | Attribute       | Description               | Notes |

+===========+=================+===========================+=======+

| module    | __doc__         | documentation string      |       |

+-----------+-----------------+---------------------------+-------+

|           | __file__        | filename (missing for     |       |

|           |                 | built-in modules)         |       |

+-----------+-----------------+---------------------------+-------+

| class     | __doc__         | documentation string      |       |

+-----------+-----------------+---------------------------+-------+

|           | __module__      | name of module in which   |       |

|           |                 | this class was defined    |       |

+-----------+-----------------+---------------------------+-------+

| method    | __doc__         | documentation string      |       |

+-----------+-----------------+---------------------------+-------+

|           | __name__        | name with which this      |       |

|           |                 | method was defined        |       |

+-----------+-----------------+---------------------------+-------+

|           | im_class        | class object that asked   | \(1)  |

|           |                 | for this method           |       |

+-----------+-----------------+---------------------------+-------+

|           | im_func or      | function object           |       |

|           | __func__        | containing implementation |       |

|           |                 | of method                 |       |

+-----------+-----------------+---------------------------+-------+

|           | im_self or      | instance to which this    |       |

|           | __self__        | method is bound, or       |       |

|           |                 | ``None``                  |       |

+-----------+-----------------+---------------------------+-------+

| function  | __doc__         | documentation string      |       |

+-----------+-----------------+---------------------------+-------+

|           | __name__        | name with which this      |       |

|           |                 | function was defined      |       |

+-----------+-----------------+---------------------------+-------+

|           | func_code       | code object containing    |       |

|           |                 | compiled function         |       |

|           |                 | :term:`bytecode`          |       |

+-----------+-----------------+---------------------------+-------+

|           | func_defaults   | tuple of any default      |       |

|           |                 | values for arguments      |       |

+-----------+-----------------+---------------------------+-------+

|           | func_doc        | (same as __doc__)         |       |

+-----------+-----------------+---------------------------+-------+

|           | func_globals    | global namespace in which |       |

|           |                 | this function was defined |       |

+-----------+-----------------+---------------------------+-------+

|           | func_name       | (same as __name__)        |       |

+-----------+-----------------+---------------------------+-------+

| generator | __iter__        | defined to support        |       |

|           |                 | iteration over container  |       |

+-----------+-----------------+---------------------------+-------+

|           | close           | raises new GeneratorExit  |       |

|           |                 | exception inside the      |       |

|           |                 | generator to terminate    |       |

|           |                 | the iteration             |       |

+-----------+-----------------+---------------------------+-------+

|           | gi_code         | code object               |       |

+-----------+-----------------+---------------------------+-------+

|           | gi_frame        | frame object or possibly  |       |

|           |                 | None once the generator   |       |

|           |                 | has been exhausted        |       |

+-----------+-----------------+---------------------------+-------+

|           | gi_running      | set to 1 when generator   |       |

|           |                 | is executing, 0 otherwise |       |

+-----------+-----------------+---------------------------+-------+

|           | next            | return the next item from |       |

|           |                 | the container             |       |

+-----------+-----------------+---------------------------+-------+

|           | send            | resumes the generator and |       |

|           |                 | "sends" a value that      |       |

|           |                 | becomes the result of the |       |

|           |                 | current yield-expression  |       |

+-----------+-----------------+---------------------------+-------+

|           | throw           | used to raise an          |       |

|           |                 | exception inside the      |       |

|           |                 | generator                 |       |

+-----------+-----------------+---------------------------+-------+

| traceback | tb_frame        | frame object at this      |       |

|           |                 | level                     |       |

+-----------+-----------------+---------------------------+-------+

|           | tb_lasti        | index of last attempted   |       |

|           |                 | instruction in bytecode   |       |

+-----------+-----------------+---------------------------+-------+

|           | tb_lineno       | current line number in    |       |

|           |                 | Python source code        |       |

+-----------+-----------------+---------------------------+-------+

|           | tb_next         | next inner traceback      |       |

|           |                 | object (called by this    |       |

|           |                 | level)                    |       |

+-----------+-----------------+---------------------------+-------+

| frame     | f_back          | next outer frame object   |       |

|           |                 | (this frame's caller)     |       |

+-----------+-----------------+---------------------------+-------+

|           | f_builtins      | built-in namespace seen   |       |

|           |                 | by this frame             |       |

+-----------+-----------------+---------------------------+-------+

|           | f_code          | code object being         |       |

|           |                 | executed in this frame    |       |

+-----------+-----------------+---------------------------+-------+

|           | f_exc_traceback | traceback if raised in    |       |

|           |                 | this frame, or ``None``   |       |

+-----------+-----------------+---------------------------+-------+

|           | f_exc_type      | exception type if raised  |       |

|           |                 | in this frame, or         |       |

|           |                 | ``None``                  |       |

+-----------+-----------------+---------------------------+-------+

|           | f_exc_value     | exception value if raised |       |

|           |                 | in this frame, or         |       |

|           |                 | ``None``                  |       |

+-----------+-----------------+---------------------------+-------+

|           | f_globals       | global namespace seen by  |       |

|           |                 | this frame                |       |

+-----------+-----------------+---------------------------+-------+

|           | f_lasti         | index of last attempted   |       |

|           |                 | instruction in bytecode   |       |

+-----------+-----------------+---------------------------+-------+

|           | f_lineno        | current line number in    |       |

|           |                 | Python source code        |       |

+-----------+-----------------+---------------------------+-------+

|           | f_locals        | local namespace seen by   |       |

|           |                 | this frame                |       |

+-----------+-----------------+---------------------------+-------+

|           | f_restricted    | 0 or 1 if frame is in     |       |

|           |                 | restricted execution mode |       |

+-----------+-----------------+---------------------------+-------+

|           | f_trace         | tracing function for this |       |

|           |                 | frame, or ``None``        |       |

+-----------+-----------------+---------------------------+-------+

| code      | co_argcount     | number of arguments (not  |       |

|           |                 | including \* or \*\*      |       |

|           |                 | args)                     |       |

+-----------+-----------------+---------------------------+-------+

|           | co_code         | string of raw compiled    |       |

|           |                 | bytecode                  |       |

+-----------+-----------------+---------------------------+-------+

|           | co_consts       | tuple of constants used   |       |

|           |                 | in the bytecode           |       |

+-----------+-----------------+---------------------------+-------+

|           | co_filename     | name of file in which     |       |

|           |                 | this code object was      |       |

|           |                 | created                   |       |

+-----------+-----------------+---------------------------+-------+

|           | co_firstlineno  | number of first line in   |       |

|           |                 | Python source code        |       |

+-----------+-----------------+---------------------------+-------+

|           | co_flags        | bitmap: 1=optimized ``|`` |       |

|           |                 | 2=newlocals ``|`` 4=\*arg |       |

|           |                 | ``|`` 8=\*\*arg           |       |

+-----------+-----------------+---------------------------+-------+

|           | co_lnotab       | encoded mapping of line   |       |

|           |                 | numbers to bytecode       |       |

|           |                 | indices                   |       |

+-----------+-----------------+---------------------------+-------+

|           | co_name         | name with which this code |       |

|           |                 | object was defined        |       |

+-----------+-----------------+---------------------------+-------+

|           | co_names        | tuple of names of local   |       |

|           |                 | variables                 |       |

+-----------+-----------------+---------------------------+-------+

|           | co_nlocals      | number of local variables |       |

+-----------+-----------------+---------------------------+-------+

|           | co_stacksize    | virtual machine stack     |       |

|           |                 | space required            |       |

+-----------+-----------------+---------------------------+-------+

|           | co_varnames     | tuple of names of         |       |

|           |                 | arguments and local       |       |

|           |                 | variables                 |       |

+-----------+-----------------+---------------------------+-------+

| builtin   | __doc__         | documentation string      |       |

+-----------+-----------------+---------------------------+-------+

|           | __name__        | original name of this     |       |

|           |                 | function or method        |       |

+-----------+-----------------+---------------------------+-------+

|           | __self__        | instance to which a       |       |

|           |                 | method is bound, or       |       |

|           |                 | ``None``                  |       |

+-----------+-----------------+---------------------------+-------+

Note:

(1)

   .. versionchanged:: 2.2

      :attr:`im_class` used to refer to the class that defined the method.

.. 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` does not return metaclass attributes when the argument

      is a class (this behavior is inherited from the :func:`dir` function).

.. function:: getmoduleinfo(path)

   Return a tuple of values that describe how Python will interpret the file

   identified by *path* if it is a module, or ``None`` if it would not be

   identified as a module.  The return tuple is ``(name, suffix, mode, mtype)``,

   where *name* is the name of the module without the name of any enclosing

   package, *suffix* is the trailing part of the file name (which may not be a

   dot-delimited extension), *mode* is the :func:`open` mode that would be used

   (``'r'`` or ``'rb'``), and *mtype* is an integer giving the type of the

   module.  *mtype* will have a value which can be compared to the constants

   defined in the :mod:`imp` module; see the documentation for that module for

   more information on module types.

   .. versionchanged:: 2.6

      Returns a :term:`named tuple` ``ModuleInfo(name, suffix, mode,

      module_type)``.

.. function:: getmodulename(path)

   Return the name of the module named by the file *path*, without including the

   names of enclosing packages.  This uses the same algorithm as the interpreter

   uses when searching for modules.  If the name cannot be matched according to the

   interpreter's rules, ``None`` is returned.

.. function:: ismodule(object)

   Return true if the object is a module.

.. function:: isclass(object)

   Return true if the object is a class.

.. function:: ismethod(object)

   Return true if the object is a method.

.. function:: isfunction(object)

   Return true if the object is a Python function or unnamed (:term:`lambda`) function.

.. function:: isgeneratorfunction(object)

   Return true if the object is a Python generator function.

   .. versionadded:: 2.6

.. function:: isgenerator(object)

   Return true if the object is a generator.

   .. versionadded:: 2.6

.. 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.

.. 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.

   .. versionadded:: 2.6

.. function:: ismethoddescriptor(object)

   Return true if the object is a method descriptor, but not if :func:`ismethod`

   or :func:`isclass` or :func:`isfunction` are true.

   This is new as of Python 2.2, and, for example, is true of

   ``int.__add__``. An object passing this test has a :attr:`__get__` attribute

   but not a :attr:`__set__` attribute, but beyond that the set of attributes

   varies.  :attr:`__name__` 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:`im_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:`__get__` and a :attr:`__set__` attribute.

   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:`__name__` and :attr:`__doc__` attributes

   (properties, getsets, and members have both of these attributes), but this is

   not guaranteed.

   .. versionadded:: 2.3

.. function:: isgetsetdescriptor(object)

   Return true if the object is a getset descriptor.

   getsets are attributes defined in extension modules via ``PyGetSetDef``

   structures.  For Python implementations without such types, this method will

   always return ``False``.

   .. versionadded:: 2.5

.. function:: ismemberdescriptor(object)

   Return true if the object is a member descriptor.

   Member descriptors are attributes defined in extension modules via

   ``PyMemberDef`` structures.  For Python implementations without such types,

   this method will always return ``False``.

   .. versionadded:: 2.5

.. _inspect-source:

Retrieving source code

----------------------

.. function:: getdoc(object)

   Get the documentation string for an object, cleaned up with :func:`cleandoc`.

.. 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).

.. 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:`IOError` is raised if the source code cannot

   be retrieved.

.. 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:`IOError` is raised if the source code

   cannot be retrieved.

.. function:: cleandoc(doc)

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

   of code.  Any whitespace that can be uniformly removed from the second line

   onwards is removed.  Also, all tabs are expanded to spaces.

   .. versionadded:: 2.6

.. _inspect-classes-functions:

Classes and functions

---------------------

.. function:: getclasstree(classes[, unique])

   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 function's arguments. A tuple of four

   things is returned: ``(args, varargs, varkw, defaults)``. *args* is a list of

   the argument names (it may contain nested lists). *varargs* and *varkw* are the

   names of the ``*`` and ``**`` arguments 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*.

   .. versionchanged:: 2.6

      Returns a :term:`named tuple` ``ArgSpec(args, varargs, keywords,

      defaults)``.

.. function:: getargvalues(frame)

   Get information about arguments passed into a particular frame. A tuple of four

   things is returned: ``(args, varargs, varkw, locals)``. *args* is a list of the

   argument names (it may contain nested lists). *varargs* and *varkw* are the

   names of the ``*`` and ``**`` arguments or ``None``. *locals* is the locals

   dictionary of the given frame.

   .. versionchanged:: 2.6

      Returns a :term:`named tuple` ``ArgInfo(args, varargs, keywords,

      locals)``.

.. function:: formatargspec(args[, varargs, varkw, defaults, formatarg, formatvarargs, formatvarkw, formatvalue, join])

   Format a pretty argument spec from the four values returned by

   :func:`getargspec`.  The format\* arguments are the corresponding optional

   formatting functions that are called to turn names and values into strings.

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

   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.

.. 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.

.. _inspect-stack:

The interpreter stack

---------------------

When the following functions return "frame records," each record is a tuple of

six items: 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.

.. warning::

   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():