8000 Mypy doesn't infer enumerate argument properly · Issue #8141 · python/mypy · GitHub
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calebho opened this issue Dec 13, 2019 · 3 comments
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Mypy doesn't infer enumerate argument properly #8141

calebho opened this issue Dec 13, 2019 · 3 comments

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@calebho
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calebho commented Dec 13, 2019

Note: if you are reporting a wrong signature of a function or a class in
the standard library, then the typeshed tracker is better suited
for this report: https://github.com/python/typeshed/issues

Please provide more information to help us understand the issue:

  • Are you reporting a bug, or opening a feature request?
    Reporting a bug
  • Please insert below the code you are checking with mypy,
    or a mock-up repro if the source is private. We would appreciate
    if you try to simplify your case to a minimal repro.
from typing import *
from itertools import product
import random

# error
a = range(2) if random.random() < .5 else product(range(2), range(2))
enumerate(a)

# ok if you give an explicit annotation
b: Union[Iterable[int], Iterable[Tuple[int, int]]] = range(2) if random.random() < .5 else product(range(2), range(2))
enumerate(b)
  • What is the actual behavior/output?
main.py:7: error: Argument 1 to "enumerate" has incompatible type "object"; expected "Iterable[<nothing>]"
  • What is the behavior/output you expect?
    No error

For version information + flags, see this playground example https://mypy-play.net/?mypy=latest&python=3.6&gist=16fc66a21fa582f9431188040f1c6bda
@calebho
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calebho commented Dec 13, 2019

I have a feeling this doesn't really depend on enumerate, but rather how the type of an if ... else expression is inferred, but I'm not 100% sure

@TH3CHARLie
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try reveal_type(a) in your code and yes it is actually because of the type of the conditional expr

@calebho
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calebho commented Dec 13, 2019

Cool looks like it's being tracked in #8074 already

@calebho calebho closed this as completed Dec 13, 2019
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