New submission from Serhiy Storchaka <[email protected]>:
Type expression is coerced to a list of parameter arguments in substitution of
ParamSpec. For example:
>>> from typing import *
>>> T = TypeVar('T')
>>> P = ParamSpec('P')
>>> C = Callable[P, T]
>>> C[int, str]
typing.Callable[[int], str]
int becomes [int]. There is even a dedicated test for this.
But it is not followed from PEP 612. Furthermore, it contradicts one of
examples in the PEP:
>>> class X(Generic[T, P]):
... f: Callable[P, int]
... x: T
...
>>> X[int, int] # Should be rejected
__main__.X[int, int]
It makes the implementation (at least the code in issue44796) more complex and
makes the user code more errorprone.
----------
messages: 398687
nosy: gvanrossum, kj, serhiy.storchaka
priority: normal
severity: normal
status: open
title: Type expression is coerced to a list of parameter arguments in
substitution of ParamSpec
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Python tracker <[email protected]>
<https://bugs.python.org/issue44801>
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