No type variables left in collections.abc.Callable

[tyleryep]

BPO	43004
Nosy	@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 = <Date 2021-01-23.04:12:23.972>
created_at = <Date 2021-01-22.20:13:42.344>
labels = ['3.9', 'type-crash']
title = 'No type variables left in collections.abc.Callable'
updated_at = <Date 2021-01-23.04:12:23.971>
user = 'https://bugs.python.org/tyleryep'

bugs.python.org fields:

activity = <Date 2021-01-23.04:12:23.971>
actor = 'tyler.yep'
assignee = 'none'
closed = True
closed_date = <Date 2021-01-23.04:12:23.972>
closer = 'tyler.yep'
components = []
creation = <Date 2021-01-22.20:13:42.344>
creator = 'tyler.yep'
dependencies = []
files = []
hgrepos = []
issue_num = 43004
keywords = []
message_count = 3.0
messages = ['385511', '385521', '385522']
nosy_count = 2.0
nosy_names = ['kj', 'tyler.yep']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue43004'
versions = ['Python 3.9']

[tyleryep]

The following code crashes when I try to run it, even though it passes when I use from typing import Callable instead.

from collections.abc import Callable
from typing import Any, TypeVar

V = TypeVar("V")
Function = Callable[[list[V], V, V], float]


def random_fn(fn: Function[Any]) -> Function[Any]:
    return fn

[Fidget-Spinner]

This seems to be a duplicate of bpo-40494. It has already been fixed in Python 3.10, and in Python 3.9.2 (which isn't out yet). You can see the what's new for it here https://docs.python.org/3/whatsnew/3.9.html#notable-changes-in-python-3-9-2.

The expected release date for Python 3.9.2 is Monday, 2021-02-15 according to PEP-596 https://www.python.org/dev/peps/pep-0596/.

For now, I guess you'll have to use the old typing.Callable, then update it in newer versions of Python.

I'm assuming you are currently using python 3.9.0/3.9.1, which has this bug. I'm unable to reproduce it on Python 3.10.

[tyleryep]

Got it, thanks!