"inspect" --- 检查对象
**********************

**源代码:** Lib/inspect.py

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

"inspect" 模块提供了一些有用的函数帮助获取对象的信息，例如模块、类、方
法、函数、回溯、帧对象以及代码对象。例如它可以帮助你检查类的内容，获取
某个方法的源代码，取得并格式化某个函数的参数列表，或者获取你需要显示的
回溯的详细信息。

该模块提供了4种主要的功能：类型检查、获取源代码、检查类与函数、检查解
释器的调用堆栈。


类型和成员
==========

"getmembers()" 函数获取对象的成员，例如类或模块。函数名以"is"开始的函
数主要作为 "getmembers()" 的第2个参数使用。它们也可用于判定某对象是否
有如下的特殊属性:

+-------------+---------------------+-----------------------------+
| 类型        | 属性                | 描述                        |
|=============|=====================|=============================|
| module 模块 | __doc__             | 文档字符串                  |
+-------------+---------------------+-----------------------------+
|             | __file__            | 文件名(内置模块没有文件名)  |
+-------------+---------------------+-----------------------------+
| class 类    | __doc__             | 文档字符串                  |
+-------------+---------------------+-----------------------------+
|             | __name__            | 类定义时所使用的名称        |
+-------------+---------------------+-----------------------------+
|             | __qualname__        | qualified name -- 限定名称  |
+-------------+---------------------+-----------------------------+
|             | __module__          | 该类型被定义时所在的模块的  |
|             |                     | 名称                        |
+-------------+---------------------+-----------------------------+
| method 方法 | __doc__             | 文档字符串                  |
+-------------+---------------------+-----------------------------+
|             | __name__            | 该方法定义时所使用的名称    |
+-------------+---------------------+-----------------------------+
|             | __qualname__        | qualified name -- 限定名称  |
+-------------+---------------------+-----------------------------+
|             | __func__            | 实现该方法的函数对象        |
+-------------+---------------------+-----------------------------+
|             | __self__            | 该方法被绑定的实例，若没有  |
|             |                     | 绑定则为 "None"             |
+-------------+---------------------+-----------------------------+
|             | __module__          | 定义此方法的模块的名称      |
+-------------+---------------------+-----------------------------+
| 函数        | __doc__             | 文档字符串                  |
+-------------+---------------------+-----------------------------+
|             | __name__            | 用于定义此函数的名称        |
+-------------+---------------------+-----------------------------+
|             | __qualname__        | qualified name -- 限定名称  |
+-------------+---------------------+-----------------------------+
|             | __code__            | 包含已编译函数的代码对象    |
|             |                     | *bytecode*                  |
+-------------+---------------------+-----------------------------+
|             | __defaults__        | 所有位置或关键字参数的默认  |
|             |                     | 值的元组                    |
+-------------+---------------------+-----------------------------+
|             | __kwdefaults__      | mapping of any default      |
|             |                     | values for keyword-only     |
|             |                     | parameters                  |
+-------------+---------------------+-----------------------------+
|             | __globals__         | global namespace in which   |
|             |                     | this function was defined   |
+-------------+---------------------+-----------------------------+
|             | __annotations__     | mapping of parameters names |
|             |                     | to annotations; ""return""  |
|             |                     | key is reserved for return  |
|             |                     | annotations.                |
+-------------+---------------------+-----------------------------+
|             | __module__          | name of module in which     |
|             |                     | this function was defined   |
+-------------+---------------------+-----------------------------+
| 回溯        | tb_frame            | 此级别的框架对象            |
+-------------+---------------------+-----------------------------+
|             | 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)      |
+-------------+---------------------+-----------------------------+
| 框架        | 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_trace             | tracing function for this   |
|             |                     | frame, or "None"            |
+-------------+---------------------+-----------------------------+
| code        | co_argcount         | number of arguments (not    |
|             |                     | including keyword only      |
|             |                     | arguments, * or ** args)    |
+-------------+---------------------+-----------------------------+
|             | co_code             | 原始编译字节码的字符串      |
+-------------+---------------------+-----------------------------+
|             | co_cellvars         | 单元变量名称的元组(通过包含 |
|             |                     | 作用域引用)                 |
+-------------+---------------------+-----------------------------+
|             | co_consts           | 字节码中使用的常量元组      |
+-------------+---------------------+-----------------------------+
|             | co_filename         | 创建此代码对象的文件的名称  |
+-------------+---------------------+-----------------------------+
|             | co_firstlineno      | number of first line in     |
|             |                     | Python source code          |
+-------------+---------------------+-----------------------------+
|             | co_flags            | bitmap of "CO_*" flags,     |
|             |                     | read more here              |
+-------------+---------------------+-----------------------------+
|             | co_lnotab           | 编码的行号到字节码索引的映  |
|             |                     | 射                          |
+-------------+---------------------+-----------------------------+
|             | co_freevars         | tuple of names of free      |
|             |                     | variables (referenced via a |
|             |                     | function's closure)         |
+-------------+---------------------+-----------------------------+
|             | co_posonlyargcount  | number of positional only   |
|             |                     | arguments                   |
+-------------+---------------------+-----------------------------+
|             | co_kwonlyargcount   | number of keyword only      |
|             |                     | arguments (not including ** |
|             |                     | arg)                        |
+-------------+---------------------+-----------------------------+
|             | co_name             | 定义此代码对象的名称        |
+-------------+---------------------+-----------------------------+
|             | co_names            | 局部变量名称的元组          |
+-------------+---------------------+-----------------------------+
|             | co_nlocals          | 局部变量的数量              |
+-------------+---------------------+-----------------------------+
|             | co_stacksize        | 需要虚拟机堆栈空间          |
+-------------+---------------------+-----------------------------+
|             | co_varnames         | 参数名和局部变量的元组      |
+-------------+---------------------+-----------------------------+
| 生成器      | __name__            | 名称                        |
+-------------+---------------------+-----------------------------+
|             | __qualname__        | qualified name -- 限定名称  |
+-------------+---------------------+-----------------------------+
|             | gi_frame            | 框架                        |
+-------------+---------------------+-----------------------------+
|             | gi_running          | 生成器在运行吗？            |
+-------------+---------------------+-----------------------------+
|             | gi_code             | code                        |
+-------------+---------------------+-----------------------------+
|             | gi_yieldfrom        | object being iterated by    |
|             |                     | "yield from", or "None"     |
+-------------+---------------------+-----------------------------+
| 协程        | __name__            | 名称                        |
+-------------+---------------------+-----------------------------+
|             | __qualname__        | qualified name -- 限定名称  |
+-------------+---------------------+-----------------------------+
|             | cr_await            | object being awaited on, or |
|             |                     | "None"                      |
+-------------+---------------------+-----------------------------+
|             | cr_frame            | 框架                        |
+-------------+---------------------+-----------------------------+
|             | cr_running          | is the coroutine running?   |
+-------------+---------------------+-----------------------------+
|             | cr_code             | code                        |
+-------------+---------------------+-----------------------------+
|             | cr_origin           | where coroutine was         |
|             |                     | created, or "None". See "s  |
|             |                     | ys.set_coroutine_origin_tr  |
|             |                     | acking_depth()"             |
+-------------+---------------------+-----------------------------+
| builtin     | __doc__             | 文档字符串                  |
+-------------+---------------------+-----------------------------+
|             | __name__            | 此函数或方法的原始名称      |
+-------------+---------------------+-----------------------------+
|             | __qualname__        | qualified name -- 限定名称  |
+-------------+---------------------+-----------------------------+
|             | __self__            | instance to which a method  |
|             |                     | is bound, or "None"         |
+-------------+---------------------+-----------------------------+

3.5 版更變: 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.

3.7 版更變: Add "cr_origin" attribute to coroutines.

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—which
   will be called with the "value" object of each member—is supplied,
   only members for which the predicate returns a true value are
   included.

   備註:

     "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 "__dir__()".

inspect.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
   "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".

   3.3 版更變: The function is based directly on "importlib".

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.

   3.8 版更變: Functions wrapped in "functools.partial()" now return
   "True" if the wrapped function is a Python generator function.

inspect.isgenerator(object)

   Return "True" if the object is a generator.

inspect.iscoroutinefunction(object)

   Return "True" if the object is a *coroutine function* (a function
   defined with an "async def" syntax).

   3.5 版新加入.

   3.8 版更變: Functions wrapped in "functools.partial()" now return
   "True" if the wrapped function is a *coroutine function*.

inspect.iscoroutine(object)

   Return "True" if the object is a *coroutine* created by an "async
   def" function.

   3.5 版新加入.

inspect.isawaitable(object)

   Return "True" if the object can be used in "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())

   3.5 版新加入.

inspect.isasyncgenfunction(object)

   Return "True" if the object is an *asynchronous generator*
   function, for example:

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

   3.6 版新加入.

   3.8 版更變: Functions wrapped in "functools.partial()" now return
   "True" if the wrapped function is a *asynchronous generator*
   function.

inspect.isasyncgen(object)

   Return "True" if the object is an *asynchronous generator iterator*
   created by an *asynchronous generator* function.

   3.6 版新加入.

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__()" 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 "__func__" attribute (etc) when an object passes
   "ismethod()".

inspect.isdatadescriptor(object)

   Return "True" if the object is a data descriptor.

   Data descriptors have a "__set__" or a "__delete__" 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.

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()". 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.

   3.5 版更變: Documentation strings are now inherited if not
   overridden.

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).  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.

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 "OSError" is raised if the source code cannot be
   retrieved.

   3.3 版更變: "OSError" is raised instead of "IOError", now an alias
   of the former.

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
   "OSError" is raised if the source code cannot be retrieved.

   3.3 版更變: "OSError" is raised instead of "IOError", now an alias
   of the former.

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.


Introspecting callables with the Signature object
=================================================

3.3 版新加入.

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

inspect.signature(callable, *, follow_wrapped=True)

   Return a "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 "functools.partial()" objects.

   Raises "ValueError" if no signature can be provided, and
   "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 the
   FAQ entry on positional-only parameters.

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

   備註:

     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 inspect.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 "Parameter" object in its "parameters" collection.

   The optional *parameters* argument is a sequence of "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 "Signature.replace()" to
   make a modified copy.

   3.5 版更變: Signature objects are picklable and hashable.

   empty

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

   parameters

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

      3.7 版更變: 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.

   return_annotation

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

   bind(*args, **kwargs)

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

   bind_partial(*args, **kwargs)

      Works the same way as "Signature.bind()", but allows the
      omission of some required arguments (mimics
      "functools.partial()" behavior.) Returns "BoundArguments", or
      raises a "TypeError" if the passed arguments do not match the
      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 "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 from_callable(obj, *, follow_wrapped=True)

      Return a "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 "Signature":

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

      3.5 版新加入.

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

   Parameter objects are *immutable*.  Instead of modifying a
   Parameter object, you can use "Parameter.replace()" to create a
   modified copy.

   3.5 版更變: Parameter objects are picklable and hashable.

   empty

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

   name

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

      **CPython implementation detail:** CPython generates implicit
      parameter names of the form ".0" on the code objects used to
      implement comprehensions and generator expressions.

      3.6 版更變: These parameter names are exposed by this module as
      names like "implicit0".

   default

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

   annotation

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

   kind

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

      +--------------------------+------------------------------------------------+
      | 名称                     | 意义                                           |
      |==========================|================================================|
      | *POSITIONAL_ONLY*        | Value must be supplied as a positional         |
      |                          | argument. Positional only parameters are those |
      |                          | which appear before a "/" entry (if present)   |
      |                          | in a Python function definition.               |
      +--------------------------+------------------------------------------------+
      | *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

   kind.description

      Describes a enum value of Parameter.kind.

      3.8 版新加入.

      Example: print all descriptions of arguments:

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

         >>> sig = signature(foo)
         >>> for param in sig.parameters.values():
         ...     print(param.kind.description)
         positional or keyword
         positional or keyword
         keyword-only
         keyword-only

   replace(*[, name][, kind][, default][, annotation])

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

   3.4 版更變: 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 inspect.BoundArguments

   Result of a "Signature.bind()" or "Signature.bind_partial()" call.
   Holds the mapping of arguments to the function's parameters.

   arguments

      A mutable mapping of parameters' names to arguments' values.
      Contains only explicitly bound arguments.  Changes in
      "arguments" will reflect in "args" and "kwargs".

      Should be used in conjunction with "Signature.parameters" for
      any argument processing purposes.

      備註:

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

      3.9 版更變: "arguments" is now of type "dict". Formerly, it was
      of type "collections.OrderedDict".

   args

      A tuple of positional arguments values.  Dynamically computed
      from the "arguments" attribute.

   kwargs

      A dict of keyword arguments values.  Dynamically computed from
      the "arguments" attribute.

   signature

      A reference to the parent "Signature" object.

   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
         {'a': 'spam', 'b': 'ham', 'args': ()}

      3.5 版新加入.

   The "args" and "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)

也參考:

  **PEP 362** - Function Signature Object.
     The detailed specification, implementation details and examples.


类与函数
========

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 parameters.
   A *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*.

   3.0 版後已棄用: Use "getfullargspec()" for an updated API that is
   usually a drop-in replacement, but also correctly handles function
   annotations and keyword-only parameters.Alternatively, use
   "signature()" and Signature Object, which provide a more structured
   introspection API for callables.

inspect.getfullargspec(func)

   Get the names and default values of a Python function's parameters.
   A *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 "signature()" and 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.

   3.4 版更變: This function is now based on "signature()", but still
   ignores "__wrapped__" attributes and includes the already bound
   first parameter in the signature output for bound methods.

   3.6 版更變: This method was previously documented as deprecated in
   favour of "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
   "getargspec()" API.

   3.7 版更變: 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.

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.

   備註:

     This function was inadvertently marked as deprecated in Python
     3.5.

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

   Format a pretty argument spec from the values returned by
   "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.

   例如:

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

   3.5 版後已棄用: Use "signature()" and Signature Object, which
   provide a better introspecting API for callables.

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.

   備註:

     This function was inadvertently marked as deprecated in Python
     3.5.

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,)}
      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'

   3.2 版新加入.

   3.5 版後已棄用: Use "Signature.bind()" and
   "Signature.bind_partial()" instead.

inspect.getclosurevars(func)

   Get the mapping of external name references in a Python function or
   method *func* to their current values. A *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.

   "TypeError" is raised if *func* is not a Python function or method.

   3.3 版新加入.

inspect.unwrap(func, *, stop=None)

   Get the object wrapped by *func*. It follows the chain of
   "__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, "signature()" uses this to stop
   unwrapping if any object in the chain has a "__signature__"
   attribute defined.

   "ValueError" is raised if a cycle is encountered.

   3.4 版新加入.


The interpreter stack
=====================

When the following functions return "frame records," each record is a
*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.

3.5 版更變: Return a named tuple instead of a tuple.

備註:

  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

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

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.

   3.5 版更變: A list of *named tuples* "FrameInfo(frame, filename,
   lineno, function, code_context, index)" is returned.

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.

   3.5 版更變: A list of *named tuples* "FrameInfo(frame, filename,
   lineno, function, code_context, index)" is returned.

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.

   3.5 版更變: A list of *named tuples* "FrameInfo(frame, filename,
   lineno, function, code_context, index)" is returned.

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.

   3.5 版更變: A list of *named tuples* "FrameInfo(frame, filename,
   lineno, function, code_context, index)" is returned.


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.

   3.2 版新加入.

"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. "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.

   3.2 版新加入.

inspect.getcoroutinestate(coroutine)

   Get current state of a coroutine object.  The function is intended
   to be used with coroutine objects created by "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.

   3.5 版新加入.

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:

inspect.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 "locals()" in
   the body of the generator, and all the same caveats apply.

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

   **CPython implementation 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.

   3.3 版新加入.

inspect.getcoroutinelocals(coroutine)

   This function is analogous to "getgeneratorlocals()", but works for
   coroutine objects created by "async def" functions.

   3.5 版新加入.


Code Objects Bit Flags
======================

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

inspect.CO_OPTIMIZED

   The code object is optimized, using fast locals.

inspect.CO_NEWLOCALS

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

inspect.CO_VARARGS

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

inspect.CO_VARKEYWORDS

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

inspect.CO_NESTED

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

inspect.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.

inspect.CO_NOFREE

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

inspect.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.

   3.5 版新加入.

inspect.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.

   3.5 版新加入.

inspect.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.

   3.6 版新加入.

備註:

  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
  "inspect" module for any introspection needs.


命令行界面
==========

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

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.

--details

   Print information about the specified object rather than the source
   code
