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

[bartvm]

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

[tscholak]

facing the same issue. do you have a workaround?

[bartvm]

Added this to .pydocstyle

[pydocstyle]
ignore-decorators = overload

We ended up adding `# noqa: F811` comments.

[sigmavirus24]

How does pydocstyle config fix a pyflakes bug?

[asottile]

I took a stab at this: #371

[feisuzhu]

Hi, it's good to see #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

[asottile]

@feisuzhu try master, I've already fixed this: #435

[eellison]

I still have this issue when the overload decorator is wrapped by another decorator.

def my_decorator(func):
    return typing.overload(func)

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

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

def utf8(value):
    pass  # actual implementation

[asottile]

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

[eellison]

Gotcha. I don't think this works either.

from typing import overload

def my_decorator(func):
    return func

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

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

def utf8(value):
    pass  # actual implementation

[asottile]

Have you tried on master? it works for me

[asottile]

actually, it even works with the released version of pyflakes so you're probably on an old one

[eellison]

This is my version info that doesn't work:

3.7.8 (flake8-comprehensions: 2.1.0, flake8-mypy: 17.8.0, mccabe: 0.6.1, pycodestyle: 2.5.0, pyflakes: 2.1.1) CPython 3.6.8 on Linux

What do you think about counting a decorator as a use of a function? Edit: the redefinition error would still exist even if the unused wouldn't

[asottile]

actually, I'm wrong about it being already released -- it is fixed on master though, please try that and confirm

[asottile]

see #435

[eellison]

yea works on master, thanks!