pyflakes: F811 (redefinition of unused variable) incorrectly triggered with @overload decorator

PEP 484 introduced the @overload decorator for type annotations.

[…] a series of @overload-decorated definitions must be followed by exactly one non-@overload-decorated definition (for the same function/method). The @overload-decorated definitions are for the benefit of the type checker only, since they will be overwritten by the non-@overload-decorated definition, while the latter is used at runtime but should be ignored by a type checker.

The following should pass PyFlakes without errors, but currently triggers F811 errors:

from typing import overload


@overload
def utf8(value: None) -> None:
    pass


@overload
def utf8(value: bytes) -> bytes:
    pass


@overload
def utf8(value: str) -> bytes:
    pass


def utf8(value):
    pass  # actual implementation

test.py:9:1: F811 redefinition of unused 'utf8' from line 4
test.py:14:1: F811 redefinition of unused 'utf8' from line 9
test.py:19:1: F811 redefinition of unused 'utf8' from line 14

About this issue

Original URL
State: closed
Created 7 years ago
Reactions: 20
Comments: 15 (8 by maintainers)

Most upvoted comments

that’s not possible to detect statically – I’d suggest not doing that (I don’t think mypy can detect that either)

I’d suggest explicitly using the overload decorator

asottile on Aug 6, 2019

yea works on master, thanks!

eellison on Aug 6, 2019

Hi, it’s good to see https://github.com/PyCQA/pyflakes/pull/371 solved this partially, but overloads on classes is still incorrectly triggered

import typing
from typing import overload


class Foo:
    @overload
    def f(self, s):  # type: (None) -> None
        pass

    @overload
    def f(self, s):  # type: (int) -> int
        pass

    def f(self, s):
        return s

    @typing.overload
    def g(self, s):  # type: (None) -> None
        pass

    @typing.overload
    def g(self, s):  # type: (int) -> int
        pass

    def g(self, s):
        return s

☁  shm  pyflakes a.py 
a.py:11: redefinition of unused 'f' from line 6
a.py:16: redefinition of unused 'f' from line 10
☁  shm  pyflakes --version
2.1.1 Python 3.6.7 on Linux

I’m now working around this by using full typing.overload name

feisuzhu on Mar 4, 2019

<strike>Added this to .pydocstyle

[pydocstyle]
ignore-decorators = overload

</strike> We ended up adding `# noqa: F811` comments.

bartvm on Feb 13, 2018

facing the same issue. do you have a workaround?

tscholak on Feb 13, 2018