10000 "incompatible type", but casting to correct type complains "redundant cast" · Issue #16385 · python/mypy · GitHub
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"incompatible type", but casting to correct type complains "redundant cast" #16385

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sliedes opened this issue Nov 1, 2023 · 1 comment
Closed

"incompatible type", but casting to correct type complains "redundant cast" #16385

sliedes opened this issue Nov 1, 2023 · 1 comment
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bug mypy got something wrong topic-casts

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@sliedes
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sliedes commented Nov 1, 2023

Bug Report

In this code, mypy --strict is unhappy both with and without a cast (playground):

from typing import cast


def foo(name: str) -> None:
    pass


def bar(
    name: str | None = None,
) -> None:
    if name is None:
        name = "foo"

    a = [lambda: foo(name)]  # incompatible type "str | None"; expected "str"
    b = [lambda: foo(cast(str, name))]  # Redundant cast to "str"

    del a, b

Expected Behavior

One of the lines should be ok for mypy.

Actual Behavior

main.py:14: error: Argument 1 to "foo" has incompatible type "str | None"; expected "str"  [arg-type]
main.py:15: error: Redundant cast to "str"  [redundant-cast]
Found 2 errors in 1 file (checked 1 source file)

Your Environment

  • Mypy version used: 1.6.1, master
  • Mypy command-line flags: --strict
  • Python version used: 3.11, 3.12
@sliedes sliedes added the bug mypy got something wrong label Nov 1, 2023
@ilevkivskyi
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This is essentially a duplicate of #4297

@ilevkivskyi ilevkivskyi closed this as not planned Won't fix, can't repro, duplicate, stale Nov 1, 2023
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@JelleZijlstra @sliedes @ilevkivskyi
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