python / python/mypy

Type check ignored on a dictionary

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#20,791 2 comments 0 reactions 0 assignees View on GitHub

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bug topic-type-context
Dominant language
Python
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Description

Bug Report

Type check is ignored on keys and values of a dictionary when declared in a specific way.

To Reproduce

playground example

Mypy detects the error whenever Util.constructor or Util.apply is not used. But if both are used the calls to f used on the keys or values are not type checked.

Expected Behavior
error: Argument 1 has incompatible type "str"; expected "int" [arg-type] at the calls of f

Actual Behavior

Mypy does not throw arg-type errors
Your Environment

checkout playground example

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 example and reproduce the case involving Util.constructor, Util.apply, and dictionary keys or values. Trace the type-checking path for the calls to f; done means mypy reports the expected incompatible str-to-int arg-type errors.

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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