[Python-Dev] PEP 362 Third Revision (original) (raw)

Yury Selivanov yselivanov at gmail.com
Thu Jun 14 13:45:28 CEST 2012

On 2012-06-14, at 12:17 AM, Nick Coghlan wrote:

On Thu, Jun 14, 2012 at 1:06 PM, Yury Selivanov <yselivanov at gmail.com> wrote:

On 2012-06-13, at 10:52 PM, Yury Selivanov wrote:

2. signature() function support all kinds of callables: classes, metaclasses, methods, class- & staticmethods, 'functools.partials', and callable objects. If a callable object has a 'signature' attribute it does a deepcopy of it before return.

Properly decorated functions are also supported. I'd like to see the "shared state" decorator from the previous thread included, as well as a short interactive interpreter session showing correct reporting of the signature of functools.partial instances.

OK. Below is how I want to update the PEP. Do you want to include anything else?

Visualizing Callable Objects' Signatures

Let's define some classes and functions:

:: from inspect import signature from functools import partial, wraps

class FooMeta(type):
    def __new__(mcls, name, bases, dct, *, bar:bool=False):
        return super().__new__(mcls, name, bases, dct)

    def __init__(cls, name, bases, dct, **kwargs):
        return super().__init__(name, bases, dct)


class Foo(metaclass=FooMeta):
    def __init__(self, spam:int=42):
        self.spam = spam

    def __call__(self, a, b, *, c) -> tuple:
        return a, b, c


def shared_vars(*shared_args):
    """Decorator factory that defines shared variables that are
       passed to every invocation of the function"""

    def decorator(f):
        @wraps(f)
        def wrapper(*args, **kwds):
            full_args = shared_args + args
            return f(*full_args, **kwds)
        # Override signature
        sig = wrapper.__signature__ = signature(f)
        for __ in shared_args:
            sig.parameters.popitem(last=False)
        return wrapper
    return decorator


@shared_vars({})
def example(_state, a, b, c):
    return _state, a, b, c


def format_signature(obj):
    return str(signature(obj))

Now, in the python REPL:

:: >>> format_signature(FooMeta) '(name, bases, dct, *, bar:bool=False)'

>>> format_signature(Foo)
'(spam:int=42)'

>>> format_signature(Foo.__call__)
'(self, a, b, *, c) -> tuple'

>>> format_signature(Foo().__call__)
'(a, b, *, c) -> tuple'

>>> format_signature(partial(Foo().__call__, 1, c=3))
'(b, *, c=3) -> tuple'

>>> format_signature(partial(partial(Foo().__call__, 1, c=3), 2, c=20))
'(*, c=20) -> tuple'

>>> format_signature(example)
'(a, b, c)'

>>> format_signature(partial(example, 1, 2))
'(c)'

>>> format_signature(partial(partial(example, 1, b=2), c=3))
'(b=2, c=3)'

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