(🎁) Support inferring type from call to `extend` when passed a non-list
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feature
topic-type-context
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
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Description
a = []
a.extend([1, 2])
reveal_type(a) # list[int]
b = [] # error: need type annotation
b.extend((1, 2))
reveal_type(b) # list[Any]
Mypy should be able to infer the type of b in this case.
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 reproducing the two examples from the issue with mypy and compare inference for list and tuple arguments passed to extend. Trace the existing handling of extend calls and add coverage for the tuple case. Done means the unannotated list is inferred as list[int] and the reveal_type result no longer reports list[Any].
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