[Python-Dev] PEP 362 Third Revision

Thu Jun 14 13:45:28 CEST 2012

On 2012年06月14日, 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年06月13日, 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)'
-
Yury