python / python/mypy

Support frozen=TYPE_CHECKING for dataclasses

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#16,224 2 comments 3 reactions 0 assignees View on GitHub

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feature topic-dataclasses
Dominant language
Python
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Description

Feature

In a project I am working on, we would like to be able to annotate dataclasses such that usually, there values should not be changed, while allowing to do so at runtime (for some construction methods and testing, more or less.

To do so, we would like to specify @dataclasses.dataclass(frozen=typing.TYPE_CHECKING)

Pitch

This could help to detect misuse of classes without introducing strict runtime guarantees.

Contributor guide

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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 by tracing mypy's handling of dataclass decorators and the typing.TYPE_CHECKING expression. Done means the proposed frozen=typing.TYPE_CHECKING form is accepted and provides static immutability checking without imposing the frozen runtime behavior.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
devtools
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
38/100

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