8000 Non overlapping inclusion check for literal types · Issue #11313 · python/mypy · GitHub
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Non overlapping inclusion check for literal types #11313

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sami-evangelista opened this issue Oct 11, 2021 · 4 comments
Open

Non overlapping inclusion check for literal types #11313

sami-evangelista opened this issue Oct 11, 2021 · 4 comments
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feature topic-literal-types topic-overlap Overlapping equality check

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@sami-evangelista
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Right now mypy spots an error on the first if condition but it would be great if it could also complain on the second one which seems a better expression of the first test:

from typing import Literal

literal_t = Literal['a', 'b', 'c']
x: literal_t = 'b'
if x == 'a' or x == 'd': ... 
if x in ('a', 'd'): ...

mypy version:

$ mypy --version
mypy 0.920+dev.bbea3b56297d3d966b9a98900c218df6616fec85
@sobolevn
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in check is not support right now, as far as I remember. It could be a cool feature. And quite easy one.
We can just translate x in ('a', 'b') expression into x == 'a' or x == 'b'. And everything should work the same way.

I will look into it.

@sobolevn
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sobolevn commented Nov 9, 2021

Turned out it is not as easy. Simple "translate" did not w 8000 ork. Several reasons:

  1. Because of how type narrowing is done in mypy
  2. Because in is not identical to two ==. There might be __contains__ defined, but not __eq__. Or they might be incompatible

@JelleZijlstra JelleZijlstra added topic-literal-types topic-overlap Overlapping equality check labels Mar 19, 2022
@intgr
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intgr commented Aug 19, 2022

This issue title is misleading, should be renamed to mention in operator, nothing to do with literal types.

@sterliakov
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Similar/duplicate of #3229?

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feature topic-literal-types topic-overlap Overlapping equality check
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@intgr @JelleZijlstra @sami-evangelista @sobolevn @sterliakov
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