28.13. "inspect" — Inspect live objects
***************************************

New in version 2.1.

**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.


28.13.1. 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                 | 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 for | (1)     |
|             |                   | this method                 |         |
+-------------+-------------------+-----------------------------+---------+
|             | im_func or        | function object containing  |         |
|             | __func__          | 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           |         |
|             |                   | *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        | builtins 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. Changed in version 2.2: "im_class" used to refer to the class that
   defined the method.

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)

   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, module_type)", 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 "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.

   Changed in version 2.6: Returns a *named tuple* "ModuleInfo(name,
   suffix, mode, module_type)".

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 or unbound 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.

   New in version 2.6.

inspect.isgenerator(object)

   Return true if the object is a generator.

   New in version 2.6.

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.

   New in version 2.6.

inspect.ismethoddescriptor(object)

   Return true if the object is a method descriptor, but not if
   "ismethod()", "isclass()", "isfunction()" or "isbuiltin()" 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 "__get__()" method
   but not a "__set__()" method, but beyond that the set of attributes
   varies.  A "__name__" attribute 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 "im_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__" 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
   "__name__" and "__doc__" attributes (properties, getsets, and
   members have both of these attributes), but this is not guaranteed.

   New in version 2.3.

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".

   New in version 2.5.

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".

   New in version 2.5.


28.13.2. 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.

   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.

   New in version 2.6.


28.13.3. Classes and functions
==============================

inspect.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.

inspect.getargspec(func)

   Get the names and default values of a Python function’s arguments.
   A tuple of four things is returned: "(args, varargs, keywords,
   defaults)". *args* is a list of the argument names (it may contain
   nested lists). *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*.

   Changed in version 2.6: Returns a *named tuple* "ArgSpec(args,
   varargs, keywords, defaults)".

inspect.getargvalues(frame)

   Get information about arguments passed into a particular frame. A
   tuple of four things is returned: "(args, varargs, keywords,
   locals)". *args* is a list of the argument names (it may contain
   nested lists). *varargs* and *keywords* are the names of the "*"
   and "**" arguments or "None". *locals* is the locals dictionary of
   the given frame.

   Changed in version 2.6: Returns a *named tuple* "ArgInfo(args,
   varargs, keywords, locals)".

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

   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, join])

   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 2.7.


28.13.4. 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])

   Get information about a frame or traceback object.  A 5-tuple is
   returned, the last five elements of the frame’s frame record.

   Changed in version 2.6: Returns a *named tuple*
   "Traceback(filename, lineno, function, code_context, index)".

inspect.getouterframes(frame[, context])

   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])

   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])

   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])

   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.
