[Python-Dev] PEP 484 wishes (original) (raw)

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.

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