diff options
Diffstat (limited to 'Doc/library/inspect.rst')
| -rw-r--r-- | Doc/library/inspect.rst | 395 |
1 files changed, 373 insertions, 22 deletions
diff --git a/Doc/library/inspect.rst b/Doc/library/inspect.rst index d127ce8cfc..d4cf9054cb 100644 --- a/Doc/library/inspect.rst +++ b/Doc/library/inspect.rst @@ -190,13 +190,26 @@ attributes: compared to the constants defined in the :mod:`imp` module; see the documentation for that module for more information on module types. + .. deprecated:: 3.3 + You may check the file path's suffix against the supported suffixes + listed in :mod:`importlib.machinery` to infer the same information. + .. 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. + names of enclosing packages. The file extension is checked against all of + the entries in :func:`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``. + + .. versionchanged:: 3.3 + This function is now based directly on :mod:`importlib` rather than the + deprecated :func:`getmoduleinfo`. .. function:: ismodule(object) @@ -355,17 +368,25 @@ Retrieving source code 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 + line of code was found. An :exc:`OSError` is raised if the source code cannot be retrieved. + .. versionchanged:: 3.3 + :exc:`OSError` is raised instead of :exc:`IOError`, now an alias of the + former. + .. 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 + returned as a single string. An :exc:`OSError` is raised if the source code cannot be retrieved. + .. versionchanged:: 3.3 + :exc:`OSError` is raised instead of :exc:`IOError`, now an alias of the + former. + .. function:: cleandoc(doc) @@ -374,6 +395,275 @@ Retrieving source code onwards is removed. Also, all tabs are expanded to spaces. +.. _inspect-signature-object: + +Introspecting callables with the Signature object +------------------------------------------------- + +.. versionadded:: 3.3 + +The Signature object represents the call signature of a callable object and its +return annotation. To retrieve a Signature object, use the :func:`signature` +function. + +.. function:: signature(callable) + + Return a :class:`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 + :func:`functools.partial` objects. + + .. note:: + + Some callables may not be introspectable in certain implementations of + Python. For example, in CPython, built-in functions defined in C provide + no metadata about their arguments. + + +.. class:: 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 + :class:`Parameter` object in its :attr:`parameters` collection. + + The optional *parameters* argument is a sequence of :class:`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 :meth:`Signature.replace` to make a + modified copy. + + .. attribute:: Signature.empty + + A special class-level marker to specify absence of a return annotation. + + .. attribute:: Signature.parameters + + An ordered mapping of parameters' names to the corresponding + :class:`Parameter` objects. + + .. attribute:: Signature.return_annotation + + The "return" annotation for the callable. If the callable has no "return" + annotation, this attribute is set to :attr:`Signature.empty`. + + .. method:: Signature.bind(*args, **kwargs) + + Create a mapping from positional and keyword arguments to parameters. + Returns :class:`BoundArguments` if ``*args`` and ``**kwargs`` match the + signature, or raises a :exc:`TypeError`. + + .. method:: Signature.bind_partial(*args, **kwargs) + + Works the same way as :meth:`Signature.bind`, but allows the omission of + some required arguments (mimics :func:`functools.partial` behavior.) + Returns :class:`BoundArguments`, or raises a :exc:`TypeError` if the + passed arguments do not match the signature. + + .. method:: 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 + :attr:`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'" + + +.. class:: Parameter(name, kind, \*, default=Parameter.empty, annotation=Parameter.empty) + + Parameter objects are *immutable*. Instead of modifying a Parameter object, + you can use :meth:`Parameter.replace` to create a modified copy. + + .. attribute:: Parameter.empty + + A special class-level marker to specify absence of default values and + annotations. + + .. attribute:: Parameter.name + + The name of the parameter as a string. Must be a valid python identifier + name (with the exception of ``POSITIONAL_ONLY`` parameters, which can have + it set to ``None``). + + .. attribute:: Parameter.default + + The default value for the parameter. If the parameter has no default + value, this attribute is set to :attr:`Parameter.empty`. + + .. attribute:: Parameter.annotation + + The annotation for the parameter. If the parameter has no annotation, + this attribute is set to :attr:`Parameter.empty`. + + .. attribute:: Parameter.kind + + Describes how argument values are bound to the parameter. Possible values + (accessible via :class:`Parameter`, like ``Parameter.KEYWORD_ONLY``): + + .. tabularcolumns:: |l|L| + + +------------------------+----------------------------------------------+ + | Name | Meaning | + +========================+==============================================+ + | *POSITIONAL_ONLY* | Value must be supplied as a positional | + | | argument. | + | | | + | | Python has no explicit syntax for defining | + | | positional-only parameters, but many built-in| + | | and extension module functions (especially | + | | those that accept only one or two parameters)| + | | accept them. | + +------------------------+----------------------------------------------+ + | *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 + + .. method:: Parameter.replace(*[, name][, kind][, default][, annotation]) + + Create a new Parameter instance based on the instance replaced was invoked + on. To override a :class:`Parameter` attribute, pass the corresponding + argument. To remove a default value or/and an annotation from a + Parameter, pass :attr:`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'" + + +.. class:: BoundArguments + + Result of a :meth:`Signature.bind` or :meth:`Signature.bind_partial` call. + Holds the mapping of arguments to the function's parameters. + + .. attribute:: BoundArguments.arguments + + An ordered, mutable mapping (:class:`collections.OrderedDict`) of + parameters' names to arguments' values. Contains only explicitly bound + arguments. Changes in :attr:`arguments` will reflect in :attr:`args` and + :attr:`kwargs`. + + Should be used in conjunction with :attr:`Signature.parameters` for any + argument processing purposes. + + .. note:: + + Arguments for which :meth:`Signature.bind` or + :meth:`Signature.bind_partial` relied on a default value are skipped. + However, if needed, it is easy to include them. + + :: + + >>> def foo(a, b=10): + ... pass + + >>> sig = signature(foo) + >>> ba = sig.bind(5) + + >>> ba.args, ba.kwargs + ((5,), {}) + + >>> for param in sig.parameters.values(): + ... if param.name not in ba.arguments: + ... ba.arguments[param.name] = param.default + + >>> ba.args, ba.kwargs + ((5, 10), {}) + + + .. attribute:: BoundArguments.args + + A tuple of positional arguments values. Dynamically computed from the + :attr:`arguments` attribute. + + .. attribute:: BoundArguments.kwargs + + A dict of keyword arguments values. Dynamically computed from the + :attr:`arguments` attribute. + + The :attr:`args` and :attr:`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) + + +.. seealso:: + + :pep:`362` - Function Signature Object. + The detailed specification, implementation details and examples. + + .. _inspect-classes-functions: Classes and functions @@ -396,9 +686,9 @@ Classes and functions :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*. + 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 @@ -414,14 +704,19 @@ Classes and functions 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 + of the ``*`` and ``**`` arguments or ``None``. *defaults* is an *n*-tuple + of the default values of the last *n* arguments, or ``None`` if there are no + default 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`. + .. note:: + Consider using the new :ref:`Signature Object <inspect-signature-object>` + interface, which provides a better way of introspecting functions. + .. function:: getargvalues(frame) @@ -432,11 +727,23 @@ Classes and functions locals dictionary of the given frame. -.. function:: formatargspec(args[, varargs, varkw, defaults, formatarg, formatvarargs, formatvarkw, formatvalue]) +.. function:: formatargspec(args[, varargs, varkw, defaults, kwonlyargs, kwonlydefaults, annotations[, formatarg, formatvarargs, formatvarkw, formatvalue, formatreturns, formatannotations]]) - 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. + Format a pretty argument spec from the values returned by + :func:`getargspec` or :func:`getfullargspec`. + + The first seven arguments are (``args``, ``varargs``, ``varkw``, + ``defaults``, ``kwonlyargs``, ``kwonlydefaults``, ``annotations``). The + other five arguments are the corresponding optional formatting functions + that are called to turn names and values into strings. The last argument + is an optional function to format the sequence of arguments. For example:: + + >>> from inspect import formatargspec, getfullargspec + >>> def f(a: int, b: float): + ... pass + ... + >>> formatargspec(*getfullargspec(f)) + '(a: int, b: float)' .. function:: formatargvalues(args[, varargs, varkw, locals, formatarg, formatvarargs, formatvarkw, formatvalue]) @@ -454,7 +761,7 @@ Classes and functions metatype is in use, cls will be the first element of the tuple. -.. function:: getcallargs(func[, *args][, **kwds]) +.. 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 @@ -468,17 +775,36 @@ Classes and functions >>> 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, 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() takes at least 1 argument (0 given) + TypeError: f() missing 1 required positional argument: 'a' .. versionadded:: 3.2 + .. note:: + Consider using the new :meth:`Signature.bind` instead. + + +.. function:: getclosurevars(func) + + Get the mapping of external name references in a Python function or + method *func* to their current values. A + :term:`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. + + :exc:`TypeError` is raised if *func* is not a Python function or method. + + .. versionadded:: 3.3 + .. _inspect-stack: @@ -589,8 +915,9 @@ but avoids executing code when it fetches attributes. that raise AttributeError). It can also return descriptors objects instead of instance members. - If the instance :attr:`__dict__` is shadowed by another member (for example a - property) then this function will be unable to find instance members. + If the instance :attr:`~object.__dict__` is shadowed by another member (for + example a property) then this function will be unable to find instance + members. .. versionadded:: 3.2 @@ -643,3 +970,27 @@ generator to be determined easily. * GEN_CLOSED: Execution has completed. .. versionadded:: 3.2 + +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: + +.. function:: 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 :func:`locals` in the body of the + generator, and all the same caveats apply. + + If *generator* is a :term:`generator` with no currently associated frame, + then an empty dictionary is returned. :exc:`TypeError` is raised if + *generator* is not a Python generator object. + + .. impl-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. + + .. versionadded:: 3.3 |