Make type refinement to work with `None in [a, b, c]`
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feature
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
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Description
Following the bug report, when checking if multiple variables are not None using the syntax None in <some_collection> mypy should be able to refine the types of these variables to non-Optional types after this check.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reading the linked bug report (mypy#17149) and trace the existing type-refinement behavior for membership checks. Done means mypy narrows the relevant variables from Optional types to non-Optional types after a None in <some_collection> check, with coverage for the reported syntax.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100