False Positive: no-member for ParamSpec under Python 3.12

[lord-haffi]

Bug description

A piece of code which worked fine for Python 3.11 (pylint v3.0.3 doesn't report anything here). But with the upgrade to 3.12 pylint suddenly doesn't know the members of ParamSpec anymore. I know that the generic typing got reworked in 3.12, maybe I'm doing something wrong. I took a quick look at the typing package in 3.12 and couldn't find any declaration of ParamSpec so it might be more a problem of the Python 3.12 release.

import inspect
from typing import Callable, TypeVar, ParamSpec

T = TypeVar("T")
P = ParamSpec("P")

def bind_arguments(func: Callable[P, T], *args: P.args, **kwargs: P.kwargs) -> inspect.BoundArguments:
    """
    Binds the given arguments to the given function. If the arguments don't match the functions signature, it will
    raise an error.
    """
    bound_arguments = inspect.signature(func).bind(*args, **kwargs)
    bound_arguments.apply_defaults()
    return bound_arguments

Configuration

No response

Command used

pylint a.py

Pylint output

************* Module a
a.py:5:48: E1101: Instance of 'ParamSpec' has no 'args' member (no-member)
a.py:5:66: E1101: Instance of 'ParamSpec' has no 'kwargs' member (no-member)

Expected behavior

No false-positive here. mypy has no complains about this code and the tests work fine under Python 3.12 as well.

Pylint version

pylint 3.0.3
astroid 3.0.1
Python 3.12.0 (tags/v3.12.0:0fb18b0, Oct  2 2023, 13:03:39) [MSC v.1935 64 bit (AMD64)]

OS / Environment

Windows 11

Additional dependencies

No response

[jacobtylerwalls]

Hi @lord-haffi, would you mind updating the snippet to include imports and assignments of P and T? Thanks!

[jacobtylerwalls]

Thanks for the report!

This diff to astroid should fix it:

diff --git a/astroid/brain/brain_typing.py b/astroid/brain/brain_typing.py
index ea496440..20276b6c 100644
--- a/astroid/brain/brain_typing.py
+++ b/astroid/brain/brain_typing.py
@@ -437,7 +437,13 @@ def _typing_transform():
     class Generic:
         @classmethod
         def __class_getitem__(cls, item):  return cls
-    class ParamSpec: ...
+    class ParamSpec:
+        @property
+        def args(self):
+            return ParamSpecArgs(self)
+        @property
+        def kwargs(self):
+            return ParamSpecKwargs(self)
     class ParamSpecArgs: ...
     class ParamSpecKwargs: ...
     class TypeAlias: ...

I took a quick look at the typing package in 3.12 and couldn't find any declaration of ParamSpec

This is exactly pylint's issue. In 3.12 CPython decided to C-accelerate the typing module, and that hosed a lot of pylint's ability to inspect typing classes. I stubbed out the bare minimum in pylint-dev/astroid@f2120db, but there's a lot missing.

[DanielNoord]

@jacobtylerwalls Is this the same issue as with collections? I thought we fixed that by making our import resolved accept the frozen modules?

[jacobtylerwalls]

I don't know what happened with collections. I'd love to know of a better solution for this, and this sounds like it.

[DanielNoord]

See pylint-dev/astroid#1512 and related PRs. We might be able to come up with a similar fix here.

[lord-haffi]

would you mind updating the snippet to include imports and assignments of P and T?

Sure! Well, you already figured it out but for the sake of completeness I edited my post.

Thanks!

[jacobtylerwalls]

@DanielNoord it's actually not as bad as the collections issue.

I looked into the reason that I stubbed out the typing module. It turns out it was really just to pass about a dozen or so cases in astroid that depend on being able to infer the bases of a class using subscript syntax. It doesn't yet work with the new PEP 695 syntax. We should fix it in a minor release when someone volunteers. In the meantime, I think my stopgap is good for a patch release.

I'll open an astroid issue with my finding.

[jacobtylerwalls]

Opened pylint-dev/astroid#2370 for the real fix. Will prepare a patch with the band-aid.