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Old-style generic ParamSpec(default=...) fails if not provided as a type argument and not in the last position of a type list when passing type arguments #138859
Description
Bug report
Bug description:
In accordance to the typing specifications, default= of ParamSpec can take an ellipsis .... However, this is not handled properly with old-style generics in the following example and causes a runtime error:
from typing import Generic, ParamSpec, TypeVar
P_default = ParamSpec("P_default", default=...)
T = TypeVar("T")
T_default = TypeVar("T_default", default=object)
class A(Generic[T, P_default, T_default]): pass>>> A[int]
Traceback (most recent call last):
...
TypeError: can only concatenate list (not "tuple") to listCPython versions tested on:
3.13
Operating systems tested on:
Linux
Linked PRs
- gh-138859: Fix
TypeErrorwhen there is aParamSpecsubstitution with a default #138867 - gh-138859: Account for
ParamSpecdefaults that are not lists … #138868 - [3.14] gh-138859: Account for
ParamSpecdefaults that are not lists … (GH-138868) #140207 - [3.13] gh-138859: Account for
ParamSpecdefaults that are not lists … (GH-138868) #140208
Activity
[-]Old-style generic `ParamSpec(default=...)` crashes if not provided as a type argument and not in the last position of a type list when passing type arguments[/-][+]Old-style generic `ParamSpec(default=...)` fails if not provided as a type argument and not in the last position of a type list when passing type arguments[/+]bzoracler commentedon Sep 13, 2025
@sobolevn I'm running the tests locally now with a fix, will make a PR in the next few minutes.
pythongh-138859: Account for `ParamSpec` defaults that are not lists …
pythongh-138859: Fix `TypeError` when there is a `ParamSpec` substitu…
sobolevn commentedon Sep 13, 2025
Oh, sorry! I've missed it. I will close my to let you contribute 👍
pythongh-138859: Account for `ParamSpec` defaults that are not lists …
gh-138859: Account for `ParamSpec` defaults that are not lists … (#13…
pythongh-138859: Account for `ParamSpec` defaults that are not lists … (
pythongh-138859: Account for `ParamSpec` defaults that are not lists … (
[3.13] gh-138859: Account for `ParamSpec` defaults that are not lists…
[3.14] gh-138859: Account for `ParamSpec` defaults that are not lists…
fix: resolve import error with python 3.13.9
fix: resolve import error with python 3.13.9
fix: resolve import error with python 3.13.9 (#1497)
pythongh-138859: Account for `ParamSpec` defaults that are not lists … (