Serhiy Storchaka <[email protected]> added the comment:
Thank you Ken Jin. So the problem is the __args__ (x, str) is interpreted
differently depending on x, and after substituting x the interpretation can be
changed. If x was ParamSpec, it was interpreted in one way, but if it becomes
int, it is now interpreted in other way.
The solution is to forbid substitution of P with wrong values (not parameters
expression). Some normalization is also needed, before and after substitution.
Other related example is:
>>> from typing import *
>>> P = ParamSpec("P")
>>> class Z(Generic[P]): pass
...
>>> A = Z[[int]]
>>> B = Z[int]
>>> A
__main__.Z[(<class 'int'>,)]
>>> B
__main__.Z[int]
>>> A.__args__
((<class 'int'>,),)
>>> B.__args__
(<class 'int'>,)
It is expected that A and B should the same.
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Python tracker <[email protected]>
<https://bugs.python.org/issue44801>
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