Substitution does not work after ParamSpec substitution of the user generic with a list of TypeVars

[serhiy-storchaka]

BPO	44802
Nosy	@gvanrossum, @serhiy-storchaka, @Fidget-Spinner

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-08-01.11:37:51.360>
labels = ['type-bug', 'library', '3.10', '3.11']
title = 'Substitution does not work after ParamSpec substitution of the user generic with a list of TypeVars'
updated_at = <Date 2021-08-01.11:37:51.360>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2021-08-01.11:37:51.360>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-08-01.11:37:51.360>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 44802
keywords = []
message_count = 1.0
messages = ['398694']
nosy_count = 3.0
nosy_names = ['gvanrossum', 'serhiy.storchaka', 'kj']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue44802'
versions = ['Python 3.10', 'Python 3.11']

Linked PRs

• gh-88965: Fix type substitution of a list of types after initial ParamSpec substitution #102808
• [3.11] gh-88965: typing: fix type substitution of a list of types after initial ParamSpec substitution (GH-102808) #102957

[serhiy-storchaka]

If the user generic with ParamSpec parameter substituted with a parametrised list containing TypeVar, that TypeVar cannot be substituted.

>>> from typing import *
>>> T = TypeVar("T")
>>> P = ParamSpec("P")
>>> class X(Generic[P]):
... f: Callable[P, int]
... 
>>> Y = X[[int, T]]
>>> Y
__main__.X[(<class 'int'>, ~T)]
>>> Y[str]
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
 File "/home/serhiy/py/cpython/Lib/typing.py", line 309, in inner
 return func(*args, **kwds)
 ^^^^^^^^^^^^^^^^^^^
 File "/home/serhiy/py/cpython/Lib/typing.py", line 1028, in __getitem__
 _check_generic(self, params, len(self.__parameters__))
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 File "/home/serhiy/py/cpython/Lib/typing.py", line 228, in _check_generic
 raise TypeError(f"{cls} is not a generic class")
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: __main__.X[(<class 'int'>, ~T)] is not a generic class

Expected result equal to X[[int, str]].

[LeeeeT]

Hi there! I'm experiencing the same issue. Will this be fixed? @serhiy-storchaka