python / python/mypy

(🐞) Variable in dataclass body has value of type `Field` when mypy thinks it's `int` (or whatever)

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#13,180 0 comments 0 reactions 0 assignees View on GitHub

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bug priority-2-low topic-dataclasses
Dominant language
Python
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Description

from dataclasses import dataclass, field

@dataclass
class A:
    a: int = field(default=1)
    print(a + 1)
  • related #13120

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First steps

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  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 provided dataclasses reproducer and run mypy on it to confirm the mismatch between the annotated int and the runtime Field value. Trace the dataclass handling that determines the type of names used in the class body, then add a regression test for this example. Done means the checker reports the class-body operation consistently with the runtime value.

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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