8000 Potential false positives with `ParamSpec "P" is unbound` after upgrading from 1.14.1 to 1.15.0 · Issue #18745 · python/mypy · GitHub
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Potential false positives with ParamSpec "P" is unbound after upgrading from 1.14.1 to 1.15.0 #18745

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alichaudry opened this issue Feb 27, 2025 · 1 comment
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Potential false positives with ParamSpec "P" is unbound after upgrading from 1.14.1 to 1.15.0 #18745

alichaudry opened this issue Feb 27, 2025 · 1 comment
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bug mypy got something wrong

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@alichaudry
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Bug Report

After upgrading to mypy 1.15.0 from mypy 1.14.1, I am now experiencing hundreds of new ParamSpec "P" is unbound errors. I imagine quite a few of these are valid, and for my use-case, I'm going to just swap how I'm (incorrectly) using ParamSpec (*args: P.args, **kwargs: P.kwargs, where P is not bound to the function in many of these cases) with a separate appropriate version (*args: object, **kwargs: object; I don't want to use Any and turn off type-checking entirely). However, I am running into cases where I think P is bound, and yet still throwing a MyPy exception.

From what I can tell, the PR which added this update may have missed my specific use-case. @sterliakov, as the author of this PR, any thoughts on my specific example? Also, would love to hear your thoughts on switching out unbound *args: P.args to *args: object instead of *args: Any. Thanks!

Example and playground gist below.

To Reproduce

from collections.abc import Callable
from functools import wraps
from typing import ParamSpec, TypeAlias

from flask import Response
from flask_login import current_user


P = ParamSpec("P")
FlaskRestfulHTTPMethodResponse: TypeAlias = tuple[Response | dict, int]
FlaskRestfulHTTPMethod: TypeAlias = Callable[P, FlaskRestfulHTTPMethodResponse]


def check_auth(f: FlaskRestfulHTTPMethod) -> FlaskRestfulHTTPMethod:
    @wraps(f)
    def wrapper(*args: P.args, **kwargs: P.kwargs) -> FlaskRestfulHTTPMethodResponse:
        if not current_user.is_authenticated:
            return {"message": "Unauthorized"}, 401
        return f(*args, **kwargs)

    return wrapper

Playground link
Gist link

Expected Behavior

Should pass the mypy checker (as it does in mypy 1.14.1).

Actual Behavior

ParamSpec "P" is unbound [valid-type]

Your Environment

  • Mypy version used: 1.15.0
  • Mypy command-line flags: N/A
  • Mypy configuration options from mypy.ini (and other config files): strict = True
  • Python version used: 3.11.4
@alichaudry alichaudry added the bug mypy got something wrong label Feb 27, 2025
@A5rocks
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A5rocks commented Feb 28, 2025

If you enable --disallow-any-generics you will get errors about missing paramspecs or typevars. In this case for instance you have:

def check_auth(f: FlaskRestfulHTTPMethod) -> FlaskRestfulHTTPMethod:

and you should instead have

def check_auth(f: FlaskRestfulHTTPMethod[P]) -> FlaskRestfulHTTPMethod[P]:

I'm surprised --strict doesn't enable that.

@A5rocks A5rocks closed this as not planned Won't fix, can't repro, duplicate, stale Feb 28, 2025
@ab5424 ab5424 mentioned this issue Mar 4, 2025
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