@overload cannot be used with conditional "if TYPE_CHECKING" #9744

blueyed · 2020-11-22T17:54:23Z

Bug Report

The handling of @overload decorators happens in (code) blocks only, which makes it not find the implementation when using:

from typing import overload
from typing import TYPE_CHECKING
from typing import Union


class K:
    if TYPE_CHECKING:
        @overload
        def foo(self, arg: int) -> int:
            ...

        @overload
        def foo(self, arg: str) -> str:
            ...

    def foo(self, arg: Union[int, str]) -> Union[int, str]:
        ...

t-overload.py:8: error: An overloaded function outside a stub file must have an implementation  [misc]
t-overload.py:16: error: Name 'foo' already defined on line 8  [no-redef]
Found 2 errors in 1 file (checked 1 source file)

I think it would be nice / feasible to merge if TYPE_CHECKING blocks maybe, so that the parser would handle it together?

mypy 0.800+dev.6e99a2db100d794b1bf900746470527cd03fce16

The text was updated successfully, but these errors were encountered:

dnaaun · 2020-11-22T21:52:25Z

I'm curious, why would you like an if TYPE_CHECKING block shielding overloads? They are ignored by the runtime anyways.

blueyed · 2020-11-23T16:17:43Z

I'm curious, why would you like an if TYPE_CHECKING block shielding overloads? They are ignored by the runtime anyways.

While it's just a dummy decorator I'd like to keep typing separate from runtime altogether.
Apart from that it just confused me initially until I've looked into how mypy parses/handles it, and was surprised to see that if blocks are considered to be separate in this regard, i.e. it looked like something that could/should get improved/fixed in mypy anyway.

altendky · 2021-01-23T19:10:07Z

I think this applies to my present issue as well. I am exploring merging trio-stubs (from trio-typing) into Trio itself and the hints for open_process() and run_process() are platform dependent.

https://github.com/python-trio/trio-typing/blob/f32f17b0f242daf2d42407f383ca581d64b6c299/trio-stubs/__init__.pyi#L567-L682
https://github.com/python-trio/trio/blob/d890affa8fed3a49b616a8fd218f4fb928bd3002/trio/_subprocess.py#L279
https://github.com/python-trio/trio/blob/d890affa8fed3a49b616a8fd218f4fb928bd3002/trio/_subprocess.py#L419-L428

hauntsaninja · 2021-01-23T19:13:58Z

For your use case you could just put the whole stub in an if TYPE_CHECKING and add a dummy implementation (def whatever(*args, **kwargs): ...) to each sys.platform branch. And then put the real implementation in the else of the if TYPE_CHECKING

altendky · 2021-01-23T19:31:42Z

Thanks for the workaround. I'll keep subscribed here in case there's a full fix. :]

cdce8p · 2021-08-02T07:41:10Z

I opened a PR a while ago that would also fix this issue. Still waiting for a review though. #10712
Maybe you would be interested to take a look, @hauntsaninja?

blueyed · 2021-09-14T20:52:41Z

@cdce8p
Thank you for fixing it!
I can confirm that it both fixes my example, and the actual use case I have at hand.

cdce8p · 2021-09-14T20:57:27Z

@blueyed Great to hear that! Unfortunately I'm still waiting for a review on the PR so no idea when it will get merged. I would be able to remove 300 lines in one file alone just from overloads I need to duplicate at the moment.

cdce8p · 2021-09-14T21:02:27Z

Sorry to bother you again @hauntsaninja. Do you have an idea who might be able to review it?

@overload

### Description This PR allows users to define overloads conditionally, e.g., based on the Python version. At the moment this is only possible if all overloads are contained in the same block which requires duplications. ```py from typing import overload, Any import sys class A: ... class B: ... if sys.version_info >= (3, 9): class C: ... @overload def func(g: int) -> A: ... @overload def func(g: bytes) -> B: ... if sys.version_info >= (3, 9): @overload def func(g: str) -> C: ... def func(g: Any) -> Any: ... ``` Closes #9744 ## Test Plan Unit tests have been added. ## Limitations Only `if` is supported. Support for `elif` and `else` might be added in the future. However, I believe that the single if as shown in the example is also the most common use case. The change itself is fully backwards compatible, i.e. the current workaround (see below) will continue to function as expected. ~~**Update**: Seems like support for `elif` and `else` is required for the tests to pass.~~ **Update**: Added support for `elif` and `else`. ## Current workaround ```py from typing import overload, Any import sys class A: ... class B: ... if sys.version_info >= (3, 9): class C: ... if sys.version_info >= (3, 9): @overload def func(g: int) -> A: ... @overload def func(g: bytes) -> B: ... @overload def func(g: str) -> C: ... def func(g: Any) -> Any: ... else: @overload def func(g: int) -> A: ... @overload def func(g: bytes) -> B: ... def func(g: Any) -> Any: ... ```

blueyed added the bug mypy got something wrong label Nov 22, 2020

blueyed mentioned this issue Dec 30, 2020

[blocked] typing: use typing.overload directly blueyed/pytest#474

Open

cdce8p mentioned this issue Aug 2, 2021

Add support for conditionally defined overloads #10712

Merged

JelleZijlstra closed this as completed in #10712 Mar 3, 2022

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@overload cannot be used with conditional "if TYPE_CHECKING" #9744

@overload cannot be used with conditional "if TYPE_CHECKING" #9744

blueyed commented Nov 22, 2020

dnaaun commented Nov 22, 2020

blueyed commented Nov 23, 2020

altendky commented Jan 23, 2021

hauntsaninja commented Jan 23, 2021 •

edited

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altendky commented Jan 23, 2021

cdce8p commented Aug 2, 2021

blueyed commented Sep 14, 2021

cdce8p commented Sep 14, 2021

cdce8p commented Sep 14, 2021

@overload cannot be used with conditional "if TYPE_CHECKING" #9744

@overload cannot be used with conditional "if TYPE_CHECKING" #9744

Comments

blueyed commented Nov 22, 2020

dnaaun commented Nov 22, 2020

blueyed commented Nov 23, 2020

altendky commented Jan 23, 2021

hauntsaninja commented Jan 23, 2021 • edited Loading

altendky commented Jan 23, 2021

cdce8p commented Aug 2, 2021

blueyed commented Sep 14, 2021

cdce8p commented Sep 14, 2021

cdce8p commented Sep 14, 2021

hauntsaninja commented Jan 23, 2021 •

edited

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