
``inspect`` --- Inspect live objects
************************************

**Source code:** Lib/inspect.py

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

The ``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.


Types and members
=================

The ``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 ``getmembers()``. They also help you determine when you can expect
to find the following special attributes:

+-------------+-------------------+-----------------------------+
| Type        | Attribute         | Description                 |
+=============+===================+=============================+
| 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                 |
+-------------+-------------------+-----------------------------+
|             | __func__          | function object containing  |
|             |                   | implementation of method    |
+-------------+-------------------+-----------------------------+
|             | __self__          | instance to which this      |
|             |                   | method is bound, or         |
|             |                   | ``None``                    |
+-------------+-------------------+-----------------------------+
| function    | __doc__           | documentation string        |
+-------------+-------------------+-----------------------------+
|             | __name__          | name with which this        |
|             |                   | function was defined        |
+-------------+-------------------+-----------------------------+
|             | __code__          | code object containing      |
|             |                   | compiled function           |
|             |                   | *bytecode*                  |
+-------------+-------------------+-----------------------------+
|             | __defaults__      | tuple of any default values |
|             |                   | for arguments               |
+-------------+-------------------+-----------------------------+
|             | __globals__       | global namespace in which   |
|             |                   | this function was defined   |
+-------------+-------------------+-----------------------------+
| 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        | builtins namespace seen by  |
|             |                   | this frame                  |
+-------------+-------------------+-----------------------------+
|             | f_code            | code object being executed  |
|             |                   | in this frame               |
+-------------+-------------------+-----------------------------+
|             | 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``       |
+-------------+-------------------+-----------------------------+

inspect.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: ``getmembers()`` does not return metaclass attributes when the
     argument is a class (this behavior is inherited from the
     ``dir()`` function).

inspect.getmoduleinfo(path)

   Returns a *named tuple* ``ModuleInfo(name, suffix, mode,
   module_type)`` 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.  In that tuple, *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 ``open()`` mode that would
   be used (``'r'`` or ``'rb'``), and *module_type* is an integer
   giving the type of the module.  *module_type* will have a value
   which can be compared to the constants defined in the ``imp``
   module; see the documentation for that module for more information
   on module types.

inspect.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.

inspect.ismodule(object)

   Return true if the object is a module.

inspect.isclass(object)

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

inspect.ismethod(object)

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

inspect.isfunction(object)

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

inspect.isgeneratorfunction(object)

   Return true if the object is a Python generator function.

inspect.isgenerator(object)

   Return true if the object is a generator.

inspect.istraceback(object)

   Return true if the object is a traceback.

inspect.isframe(object)

   Return true if the object is a frame.

inspect.iscode(object)

   Return true if the object is a code.

inspect.isbuiltin(object)

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

inspect.isroutine(object)

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

inspect.isabstract(object)

   Return true if the object is an abstract base class.

inspect.ismethoddescriptor(object)

   Return true if the object is a method descriptor, but not if
   ``ismethod()``, ``isclass()``, ``isfunction()`` or ``isbuiltin()``
   are true.

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

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

inspect.isdatadescriptor(object)

   Return true if the object is a data descriptor.

   Data descriptors have both a ``__get__`` and a ``__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
   ``__name__`` and ``__doc__`` attributes (properties, getsets, and
   members have both of these attributes), but this is not guaranteed.

inspect.isgetsetdescriptor(object)

   Return true if the object is a getset descriptor.

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

inspect.ismemberdescriptor(object)

   Return true if the object is a member descriptor.

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


Retrieving source code
======================

inspect.getdoc(object)

   Get the documentation string for an object, cleaned up with
   ``cleandoc()``.

inspect.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).

inspect.getfile(object)

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

inspect.getmodule(object)

   Try to guess which module an object was defined in.

inspect.getsourcefile(object)

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

inspect.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 ``IOError`` is raised if the source code cannot be
   retrieved.

inspect.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
   ``IOError`` is raised if the source code cannot be retrieved.

inspect.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.


Classes and functions
=====================

inspect.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.

inspect.getargspec(func)

   Get the names and default values of a Python function's arguments.
   A *named tuple* ``ArgSpec(args, varargs, keywords, defaults)`` is
   returned. *args* is a list of the argument names. *varargs* and
   *keywords* 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*.

   Deprecated since version 3.0: Use ``getfullargspec()`` instead,
   which provides information about keyword-only arguments and
   annotations.

inspect.getfullargspec(func)

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

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

   *args* is a list of the argument names.  *varargs* and *varkw* are
   the names of the ``*`` and ``**`` arguments or ``None``.
   *defaults* is an n-tuple of the default values of the last n
   arguments.  *kwonlyargs* is a list of keyword-only argument names.
   *kwonlydefaults* is a dictionary mapping names from kwonlyargs to
   defaults.  *annotations* is a dictionary mapping argument names to
   annotations.

   The first four items in the tuple correspond to ``getargspec()``.

inspect.getargvalues(frame)

   Get information about arguments passed into a particular frame.  A
   *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.

inspect.formatargspec(args[, varargs, varkw, defaults, formatarg, formatvarargs, formatvarkw, formatvalue])

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

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

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

inspect.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.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,)}
      >>> getcallargs(f, a=2, x=4)
      {'a': 2, 'named': {'x': 4}, 'b': 1, 'pos': ()}
      >>> getcallargs(f)
      Traceback (most recent call last):
      ...
      TypeError: f() takes at least 1 argument (0 given)

   New in version 3.2.


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.

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 ``finally`` clause.  This is also important
  if the cycle detector was disabled when Python was compiled or using
  ``gc.disable()``.  For example:

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

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.

inspect.getframeinfo(frame, context=1)

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

inspect.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.

inspect.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.

inspect.currentframe()

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

   **CPython implementation 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``.

inspect.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.

inspect.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.


Fetching attributes statically
==============================

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

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

inspect.getattr_static(obj, attr, default=None)

   Retrieve attributes without triggering dynamic lookup via the
   descriptor protocol, ``__getattr__()`` or ``__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 ``__dict__`` is shadowed by another member (for
   example a property) then this function will be unable to find
   instance members.

   New in version 3.2.

``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 a Generator
============================

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. ``getgeneratorstate()`` allows the current state of a
generator to be determined easily.

inspect.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.

   New in version 3.2.
