Lib/inspect.py (part 3)

Source:

cpython 3.14 @ ab2d84fe1023/Lib/inspect.py ↗

This annotation covers signature introspection. See lib_inspect2_detail for getfile, getsource, getclosurevars, getfullargspec, and frame inspection.

Map

Lines	Symbol	Role
1-80	signature	Return a Signature for any callable
81-180	Parameter	Represents one parameter with kind, default, annotation
181-260	BoundArguments	Result of Signature.bind
261-360	getmembers	List (name, value) pairs for an object
361-500	getmodule	Find what module defined an object

Reading

signature

# CPython: Lib/inspect.py:3180 signature
def signature(obj, *, follow_wrapped=True, globals=None, locals=None, eval_str=False):
    if not callable(obj):
        raise TypeError(f'{obj!r} is not a callable object')
    if isinstance(obj, types.MethodType):
        sig = signature(obj.__func__, follow_wrapped=follow_wrapped, ...)
        return _signature_bound_method(sig)
    if isinstance(obj, functools.partial):
        sig = signature(obj.func, ...)
        return _signature_get_partial(sig, obj)
    if isinstance(obj, types.FunctionType):
        return Signature.from_function(obj, ...)
    if hasattr(obj, '__signature__'):
        return obj.__signature__
    ...

signature dispatches by callable type. Methods drop self. functools.partial adjusts the signature by removing pre-filled parameters. Custom callables can set __signature__ to override introspection.

Parameter

# CPython: Lib/inspect.py:2560 Parameter.__init__
class Parameter:
    POSITIONAL_ONLY = _ParameterKind.POSITIONAL_ONLY
    POSITIONAL_OR_KEYWORD = _ParameterKind.POSITIONAL_OR_KEYWORD
    VAR_POSITIONAL = _ParameterKind.VAR_POSITIONAL
    KEYWORD_ONLY = _ParameterKind.KEYWORD_ONLY
    VAR_KEYWORD = _ParameterKind.VAR_KEYWORD
    empty = _empty

    def __init__(self, name, kind, *, default=_empty, annotation=_empty):
        if kind not in _ParameterKind:
            raise ValueError(f'invalid value for "kind" attribute')
        if default is not _empty and kind in (_VAR_POSITIONAL, _VAR_KEYWORD):
            raise ValueError(f'{kind.description} parameters cannot have default values')
        ...

POSITIONAL_ONLY parameters are before / in the signature. KEYWORD_ONLY parameters are after * or *args. VAR_POSITIONAL is *args, VAR_KEYWORD is **kwargs. Parameter.empty is the sentinel for "no default" and "no annotation".

BoundArguments

# CPython: Lib/inspect.py:2920 Signature.bind
class Signature:
    def bind(self, *args, **kwargs):
        arguments = {}
        ...
        for param in self.parameters.values():
            if param.kind == _POSITIONAL_OR_KEYWORD:
                if args:
                    arguments[param.name] = args[0]
                    args = args[1:]
                elif param.name in kwargs:
                    arguments[param.name] = kwargs.pop(param.name)
                elif param.default is not _empty:
                    pass  # Default used; not in arguments
                else:
                    raise TypeError(f"missing a required argument: '{param.name}'")
        return BoundArguments(self, arguments)

sig.bind(1, 2, x=3) returns a BoundArguments where arguments maps parameter names to values. apply_defaults() fills in defaults. Used by functools.wraps to forward calls.

gopy notes

signature is module/inspect.Signature in module/inspect/module.go. Parameter is a Go struct. Signature.bind iterates parameters matching args/kwargs, building a Go map[string]objects.Object.