Arguments ignored in substitution in typing.Callable

[serhiy-storchaka]

BPO	44793
Nosy	@gvanrossum, @serhiy-storchaka, @miss-islington, @Fidget-Spinner
PRs	bpo-44793: Fix checking the number of arguments when subscribe a gene… #27515 [3.10] bpo-44793: Fix checking the number of arguments when subscribe a generic type with ParamSpec parameter. (GH-27515) #27537

^{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 = <Date 2021-08-02.07:32:47.001>
created_at = <Date 2021-07-31.12:24:26.513>
labels = ['type-bug', 'library', '3.10', '3.11']
title = 'Arguments ignored in substitution in typing.Callable'
updated_at = <Date 2021-08-02.07:32:47.000>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2021-08-02.07:32:47.000>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2021-08-02.07:32:47.001>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2021-07-31.12:24:26.513>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 44793
keywords = ['patch']
message_count = 5.0
messages = ['398636', '398648', '398656', '398728', '398730']
nosy_count = 4.0
nosy_names = ['gvanrossum', 'serhiy.storchaka', 'miss-islington', 'kj']
pr_nums = ['27515', '27537']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue44793'
versions = ['Python 3.10', 'Python 3.11']

[serhiy-storchaka]

>>> import typing
>>> T = typing.TypeVar('T')
>>> P = typing.ParamSpec('P')
>>> C = typing.Callable[P, T]
>>> C[int, str, float]
typing.Callable[[int], str]

int substitutes P as [int], str substitutes T, and the third argument float is ignored.

[serhiy-storchaka]

If Callable is nested, it works as expected:

>>> typing.List[C][int, str, float]
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 231, in _check_generic
    raise TypeError(f"Too {'many' if alen > elen else 'few'} parameters for {cls};"
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: Too many parameters for typing.List[typing.Callable[~P, ~T]]; actual 3, expected 2

collections.abc.Callable raises an error too.

[serhiy-storchaka]

There is also similar bug in Generic:

>>> from typing import *
>>> T = TypeVar("T")
>>> P = ParamSpec("P")
>>> class X(Generic[T, P]):
...     f: Callable[P, int]
...     x: T
... 
>>> P_2 = ParamSpec("P_2")
>>> X[int, P_2, str]
__main__.X[int, ~P_2]

[serhiy-storchaka]

New changeset f92b913 by Serhiy Storchaka in branch 'main':
bpo-44793: Fix checking the number of arguments when subscribe a generic type with ParamSpec parameter. (GH-27515)
f92b913

[miss-islington]

New changeset c8db292 by Miss Islington (bot) in branch '3.10':
bpo-44793: Fix checking the number of arguments when subscribe a generic type with ParamSpec parameter. (GH-27515)
c8db292