python / python/mypy

bogus complaint when checking Callable arguments

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bug topic-type-context topic-type-variables
Dominant language
Python
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Description

Bug Report

mypy complains about correct code. it confuses the arguments to a Callable parameter with the return value of the function.

To Reproduce

https://gist.github.com/mypy-play/59b8705d6737e1f8f4855d7b2270e7e9

Expected Behavior

Code checks OK.

Actual Behavior

Bogus error:
Argument 1 to "test" has incompatible type "Callable[[str], bool]"; expected "Callable[[float | str], bool]" [arg-type]

Your Environment

mypy 1.15.0 (compiled: yes)
Python 3.13.2

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the linked mypy-play reproduction and run it using mypy 1.15.0 on Python 3.13.2. Investigate why the Callable argument is compared against the function's return value; done means the reproduction type-checks without the reported arg-type error.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
devtools
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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