| :mod:`inspect` --- Inspect live objects |
| ======================================= |
| |
| .. module:: inspect |
| :synopsis: Extract information and source code from live objects. |
| .. moduleauthor:: Ka-Ping Yee <ping@lfw.org> |
| .. sectionauthor:: Ka-Ping Yee <ping@lfw.org> |
| |
| **Source code:** :source:`Lib/inspect.py` |
| |
| -------------- |
| |
| The :mod:`inspect` module provides several useful functions to help get |
| information about live objects such as modules, classes, methods, functions, |
| tracebacks, frame objects, and code objects. For example, it can help you |
| examine the contents of a class, retrieve the source code of a method, extract |
| and format the argument list for a function, or get all the information you need |
| to display a detailed traceback. |
| |
| There are four main kinds of services provided by this module: type checking, |
| getting source code, inspecting classes and functions, and examining the |
| interpreter stack. |
| |
| |
| .. _inspect-types: |
| |
| Types and members |
| ----------------- |
| |
| The :func:`getmembers` function retrieves the members of an object such as a |
| class or module. The sixteen functions whose names begin with "is" are mainly |
| provided as convenient choices for the second argument to :func:`getmembers`. |
| They also help you determine when you can expect to find the following special |
| attributes: |
| |
| +-----------+-----------------+---------------------------+ |
| | Type | Attribute | Description | |
| +===========+=================+===========================+ |
| | 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 | |
| | | | :term:`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`` | |
| +-----------+-----------------+---------------------------+ |
| |
| |
| .. function:: getmembers(object[, predicate]) |
| |
| Return all the members of an object in a list of (name, value) pairs sorted by |
| name. If the optional *predicate* argument is supplied, only members for which |
| the predicate returns a true value are included. |
| |
| .. note:: |
| |
| :func:`getmembers` does not return metaclass attributes when the argument |
| is a class (this behavior is inherited from the :func:`dir` function). |
| |
| |
| .. function:: getmoduleinfo(path) |
| |
| Returns a :term:`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 :func:`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 :mod:`imp` module; see the |
| documentation for that module for more information on module types. |
| |
| |
| .. function:: getmodulename(path) |
| |
| Return the name of the module named by the file *path*, without including the |
| names of enclosing packages. This uses the same algorithm as the interpreter |
| uses when searching for modules. If the name cannot be matched according to the |
| interpreter's rules, ``None`` is returned. |
| |
| |
| .. function:: ismodule(object) |
| |
| Return true if the object is a module. |
| |
| |
| .. function:: isclass(object) |
| |
| Return true if the object is a class, whether built-in or created in Python |
| code. |
| |
| |
| .. function:: ismethod(object) |
| |
| Return true if the object is a bound method written in Python. |
| |
| |
| .. function:: isfunction(object) |
| |
| Return true if the object is a Python function, which includes functions |
| created by a :term:`lambda` expression. |
| |
| |
| .. function:: isgeneratorfunction(object) |
| |
| Return true if the object is a Python generator function. |
| |
| |
| .. function:: isgenerator(object) |
| |
| Return true if the object is a generator. |
| |
| |
| .. function:: istraceback(object) |
| |
| Return true if the object is a traceback. |
| |
| |
| .. function:: isframe(object) |
| |
| Return true if the object is a frame. |
| |
| |
| .. function:: iscode(object) |
| |
| Return true if the object is a code. |
| |
| |
| .. function:: isbuiltin(object) |
| |
| Return true if the object is a built-in function or a bound built-in method. |
| |
| |
| .. function:: isroutine(object) |
| |
| Return true if the object is a user-defined or built-in function or method. |
| |
| |
| .. function:: isabstract(object) |
| |
| Return true if the object is an abstract base class. |
| |
| |
| .. function:: ismethoddescriptor(object) |
| |
| Return true if the object is a method descriptor, but not if |
| :func:`ismethod`, :func:`isclass`, :func:`isfunction` or :func:`isbuiltin` |
| are true. |
| |
| This, for example, is true of ``int.__add__``. An object passing this test |
| has a :attr:`__get__` attribute but not a :attr:`__set__` attribute, but |
| beyond that the set of attributes varies. :attr:`__name__` is usually |
| sensible, and :attr:`__doc__` often is. |
| |
| Methods implemented via descriptors that also pass one of the other tests |
| return false from the :func:`ismethoddescriptor` test, simply because the |
| other tests promise more -- you can, e.g., count on having the |
| :attr:`__func__` attribute (etc) when an object passes :func:`ismethod`. |
| |
| |
| .. function:: isdatadescriptor(object) |
| |
| Return true if the object is a data descriptor. |
| |
| Data descriptors have both a :attr:`__get__` and a :attr:`__set__` attribute. |
| Examples are properties (defined in Python), getsets, and members. The |
| latter two are defined in C and there are more specific tests available for |
| those types, which is robust across Python implementations. Typically, data |
| descriptors will also have :attr:`__name__` and :attr:`__doc__` attributes |
| (properties, getsets, and members have both of these attributes), but this is |
| not guaranteed. |
| |
| |
| .. function:: isgetsetdescriptor(object) |
| |
| Return true if the object is a getset descriptor. |
| |
| .. impl-detail:: |
| |
| getsets are attributes defined in extension modules via |
| :c:type:`PyGetSetDef` structures. For Python implementations without such |
| types, this method will always return ``False``. |
| |
| |
| .. function:: ismemberdescriptor(object) |
| |
| Return true if the object is a member descriptor. |
| |
| .. impl-detail:: |
| |
| Member descriptors are attributes defined in extension modules via |
| :c:type:`PyMemberDef` structures. For Python implementations without such |
| types, this method will always return ``False``. |
| |
| |
| .. _inspect-source: |
| |
| Retrieving source code |
| ---------------------- |
| |
| .. function:: getdoc(object) |
| |
| Get the documentation string for an object, cleaned up with :func:`cleandoc`. |
| |
| |
| .. function:: getcomments(object) |
| |
| Return in a single string any lines of comments immediately preceding the |
| object's source code (for a class, function, or method), or at the top of the |
| Python source file (if the object is a module). |
| |
| |
| .. function:: getfile(object) |
| |
| Return the name of the (text or binary) file in which an object was defined. |
| This will fail with a :exc:`TypeError` if the object is a built-in module, |
| class, or function. |
| |
| |
| .. function:: getmodule(object) |
| |
| Try to guess which module an object was defined in. |
| |
| |
| .. function:: getsourcefile(object) |
| |
| Return the name of the Python source file in which an object was defined. This |
| will fail with a :exc:`TypeError` if the object is a built-in module, class, or |
| function. |
| |
| |
| .. function:: getsourcelines(object) |
| |
| Return a list of source lines and starting line number for an object. The |
| argument may be a module, class, method, function, traceback, frame, or code |
| object. The source code is returned as a list of the lines corresponding to the |
| object and the line number indicates where in the original source file the first |
| line of code was found. An :exc:`IOError` is raised if the source code cannot |
| be retrieved. |
| |
| |
| .. function:: getsource(object) |
| |
| Return the text of the source code for an object. The argument may be a module, |
| class, method, function, traceback, frame, or code object. The source code is |
| returned as a single string. An :exc:`IOError` is raised if the source code |
| cannot be retrieved. |
| |
| |
| .. function:: cleandoc(doc) |
| |
| Clean up indentation from docstrings that are indented to line up with blocks |
| of code. Any whitespace that can be uniformly removed from the second line |
| onwards is removed. Also, all tabs are expanded to spaces. |
| |
| |
| .. _inspect-classes-functions: |
| |
| Classes and functions |
| --------------------- |
| |
| .. function:: getclasstree(classes, unique=False) |
| |
| Arrange the given list of classes into a hierarchy of nested lists. Where a |
| nested list appears, it contains classes derived from the class whose entry |
| immediately precedes the list. Each entry is a 2-tuple containing a class and a |
| tuple of its base classes. If the *unique* argument is true, exactly one entry |
| appears in the returned structure for each class in the given list. Otherwise, |
| classes using multiple inheritance and their descendants will appear multiple |
| times. |
| |
| |
| .. function:: getargspec(func) |
| |
| Get the names and default values of a Python function's arguments. A |
| :term:`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:: 3.0 |
| Use :func:`getfullargspec` instead, which provides information about |
| keyword-only arguments and annotations. |
| |
| |
| .. function:: getfullargspec(func) |
| |
| Get the names and default values of a Python function's arguments. A |
| :term:`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 :func:`getargspec`. |
| |
| |
| .. function:: getargvalues(frame) |
| |
| Get information about arguments passed into a particular frame. A |
| :term:`named tuple` ``ArgInfo(args, varargs, keywords, locals)`` is |
| returned. *args* is a list of the argument names. *varargs* and *keywords* |
| are the names of the ``*`` and ``**`` arguments or ``None``. *locals* is the |
| locals dictionary of the given frame. |
| |
| |
| .. function:: formatargspec(args[, varargs, varkw, defaults, formatarg, formatvarargs, formatvarkw, formatvalue]) |
| |
| Format a pretty argument spec from the four values returned by |
| :func:`getargspec`. The format\* arguments are the corresponding optional |
| formatting functions that are called to turn names and values into strings. |
| |
| |
| .. function:: formatargvalues(args[, varargs, varkw, locals, formatarg, formatvarargs, formatvarkw, formatvalue]) |
| |
| Format a pretty argument spec from the four values returned by |
| :func:`getargvalues`. The format\* arguments are the corresponding optional |
| formatting functions that are called to turn names and values into strings. |
| |
| |
| .. function:: getmro(cls) |
| |
| Return a tuple of class cls's base classes, including cls, in method resolution |
| order. No class appears more than once in this tuple. Note that the method |
| resolution order depends on cls's type. Unless a very peculiar user-defined |
| metatype is in use, cls will be the first element of the tuple. |
| |
| |
| .. function:: getcallargs(func[, *args][, **kwds]) |
| |
| Bind the *args* and *kwds* to the argument names of the Python function or |
| method *func*, as if it was called with them. For bound methods, bind also the |
| first argument (typically named ``self``) to the associated instance. A dict |
| is returned, mapping the argument names (including the names of the ``*`` and |
| ``**`` arguments, if any) to their values from *args* and *kwds*. In case of |
| invoking *func* incorrectly, i.e. whenever ``func(*args, **kwds)`` would raise |
| an exception because of incompatible signature, an exception of the same type |
| and the same or similar message is raised. For example:: |
| |
| >>> from inspect import getcallargs |
| >>> def f(a, b=1, *pos, **named): |
| ... pass |
| >>> getcallargs(f, 1, 2, 3) |
| {'a': 1, 'named': {}, 'b': 2, 'pos': (3,)} |
| >>> 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) |
| |
| .. versionadded:: 3.2 |
| |
| |
| .. _inspect-stack: |
| |
| The interpreter stack |
| --------------------- |
| |
| When the following functions return "frame records," each record is a tuple of |
| six items: the frame object, the filename, the line number of the current line, |
| the function name, a list of lines of context from the source code, and the |
| index of the current line within that list. |
| |
| .. note:: |
| |
| Keeping references to frame objects, as found in the first element of the frame |
| records these functions return, can cause your program to create reference |
| cycles. Once a reference cycle has been created, the lifespan of all objects |
| which can be accessed from the objects which form the cycle can become much |
| longer even if Python's optional cycle detector is enabled. If such cycles must |
| be created, it is important to ensure they are explicitly broken to avoid the |
| delayed destruction of objects and increased memory consumption which occurs. |
| |
| Though the cycle detector will catch these, destruction of the frames (and local |
| variables) can be made deterministic by removing the cycle in a |
| :keyword:`finally` clause. This is also important if the cycle detector was |
| disabled when Python was compiled or using :func:`gc.disable`. For example:: |
| |
| def handle_stackframe_without_leak(): |
| frame = inspect.currentframe() |
| try: |
| # do something with the frame |
| finally: |
| del frame |
| |
| The optional *context* argument supported by most of these functions specifies |
| the number of lines of context to return, which are centered around the current |
| line. |
| |
| |
| .. function:: getframeinfo(frame, context=1) |
| |
| Get information about a frame or traceback object. A :term:`named tuple` |
| ``Traceback(filename, lineno, function, code_context, index)`` is returned. |
| |
| |
| .. function:: getouterframes(frame, context=1) |
| |
| Get a list of frame records for a frame and all outer frames. These frames |
| represent the calls that lead to the creation of *frame*. The first entry in the |
| returned list represents *frame*; the last entry represents the outermost call |
| on *frame*'s stack. |
| |
| |
| .. function:: getinnerframes(traceback, context=1) |
| |
| Get a list of frame records for a traceback's frame and all inner frames. These |
| frames represent calls made as a consequence of *frame*. The first entry in the |
| list represents *traceback*; the last entry represents where the exception was |
| raised. |
| |
| |
| .. function:: currentframe() |
| |
| Return the frame object for the caller's stack frame. |
| |
| .. impl-detail:: |
| |
| This function relies on Python stack frame support in the interpreter, |
| which isn't guaranteed to exist in all implementations of Python. If |
| running in an implementation without Python stack frame support this |
| function returns ``None``. |
| |
| |
| .. function:: stack(context=1) |
| |
| Return a list of frame records for the caller's stack. The first entry in the |
| returned list represents the caller; the last entry represents the outermost |
| call on the stack. |
| |
| |
| .. function:: trace(context=1) |
| |
| Return a list of frame records for the stack between the current frame and the |
| frame in which an exception currently being handled was raised in. The first |
| entry in the list represents the caller; the last entry represents where the |
| exception was raised. |
| |
| |
| Fetching attributes statically |
| ------------------------------ |
| |
| Both :func:`getattr` and :func:`hasattr` can trigger code execution when |
| fetching or checking for the existence of attributes. Descriptors, like |
| properties, will be invoked and :meth:`__getattr__` and :meth:`__getattribute__` |
| may be called. |
| |
| For cases where you want passive introspection, like documentation tools, this |
| can be inconvenient. `getattr_static` has the same signature as :func:`getattr` |
| but avoids executing code when it fetches attributes. |
| |
| .. function:: getattr_static(obj, attr, default=None) |
| |
| Retrieve attributes without triggering dynamic lookup via the |
| descriptor protocol, `__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. |
| |
| .. versionadded:: 3.2 |
| |
| The only known case that can cause `getattr_static` to trigger code execution, |
| and cause it to return incorrect results (or even break), is where a class uses |
| :data:`~object.__slots__` and provides a `__dict__` member using a property or |
| descriptor. If you find other cases please report them so they can be fixed |
| or documented. |
| |
| `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. :func:`getgeneratorstate` allows the current state of a |
| generator to be determined easily. |
| |
| .. function:: getgeneratorstate(generator) |
| |
| Get current state of a generator-iterator. |
| |
| Possible states are: |
| * GEN_CREATED: Waiting to start execution. |
| * GEN_RUNNING: Currently being executed by the interpreter. |
| * GEN_SUSPENDED: Currently suspended at a yield expression. |
| * GEN_CLOSED: Execution has completed. |
| |
| .. versionadded:: 3.2 |