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nested isinstances lose type information #10146

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Akuli opened this issue Feb 27, 2021 · 2 comments
Open

nested isinstances lose type information #10146

Akuli opened this issue Feb 27, 2021 · 2 comments
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bug mypy got something wrong false-positive mypy gave an error on correct code topic-join-v-union Using join vs. using unions topic-type-narrowing Conditional type narrowing / binder topic-union-types

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@Akuli
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Akuli commented Feb 27, 2021

Bug Report

To Reproduce

x = object()
if isinstance(x, (int, str)):
    reveal_type(x)      # Union[int, str]
    if isinstance(x, int):
        pass
    reveal_type(x)      # object

Expected Behavior

both types revealed as Union[int, str]

Actual Behavior

object from second type

Your Environment

  • Mypy version used: latest master (0.820+dev.72ac2cee910ca61bfdf449217328b6d10b45d378)
  • Mypy command-line flags: none
  • Mypy configuration options from mypy.ini (and other config files): none
  • Python version used: 3.7.3
  • Operating system and version: debian 10 based linux distro
@Akuli Akuli added the bug mypy got something wrong label Feb 27, 2021
@JukkaL JukkaL added false-positive mypy gave an error on correct code topic-union-types labels Mar 5, 2021
@JukkaL
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JukkaL commented Mar 5, 2021

It looks like we should perhaps maintain a stack of narrowed down types (though I might be wrong).

@AlexWaygood AlexWaygood added the topic-type-narrowing Conditional type narrowing / binder label Apr 4, 2022
@erictraut
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This is another example of join vs union. It should probably be tagged as such.

@hauntsaninja hauntsaninja added the topic-join-v-union Using join vs. using unions label Aug 12, 2023
@devRD devRD mentioned this issue Sep 24, 2023
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bug mypy got something wrong false-positive mypy gave an error on correct code topic-join-v-union Using join vs. using unions topic-type-narrowing Conditional type narrowing / binder topic-union-types
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@JukkaL @erictraut @hauntsaninja @Akuli @AlexWaygood