python / python/mypy

no error when using `field` outside of a `dataclass`

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#13,120 2 comments 2 reactions 0 assignees View on GitHub

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

from dataclasses import field

a = field(default=1)

a + 1  # runtime error
reveal_type(a)  # int

playground

Contributor guide

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First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the issue with the Python snippet or linked mypy playground, then trace how dataclasses.field is analyzed outside a dataclass context. Done means mypy reports the invalid use instead of accepting a value that runtime treats as a field object, while preserving valid dataclass usage.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
compilers, devtools
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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