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[Python-Dev] PEP 484 wishes

Guido van Rossum guido at python.org
Mon May 18 01:50:22 CEST 2015 
On Sun, May 17, 2015 at 3:07 PM, Alex Grönholm <alex.gronholm at nextday.fi>
wrote:

>  Looking at PEP 484, I came up with two use cases that I felt were not
> catered for:
>
>    1. Specifying that a parameter should be a subclass of another
>    (example: Type[dict] would match dict or OrderedDict; plain "Type" would
>    equal "type" from builtins)
>
>
I don't understand. What is "Type"? Can you work this out in a full
example? This code is already okay:

def foo(a: dict):
    ...

foo(OrderedDict())


>
>    1. Specifying that a callable should take at least the specified
>    arguments but would not be limited to them: Callable[[str, int, ...], Any]
>
> Case #2 works already (Callable[[str, int], Any] if the unspecified
> arguments are optional, but not if they're mandatory. Any thoughts?
>
For #2 we explicitly debated this and found that there aren't use cases
known that are strong enough to need additional flexibility in the args of
a callable. (How is the code calling the callable going to know what
arguments are safe to pass?) If there really is a need we can address in a
future revision.

-- 
--Guido van Rossum (python.org/~guido)
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