Poor handling of `attr`s converters.
Open
Nobody has claimed this yet.
bug
false-positive
topic-attrs
- Dominant language
- Python
- Stars
- 20.6k
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Description
When running mypy over the following file:
from typing import Sequence
import attr
@attr.s
class A:
a: Sequence[str] = attr.ib(converter=list)
A(["a"])
I get:
$ mypy a.py
a.py:7: error: List item 0 has incompatible type "str"; expected "_T"
which is a little confusing, because str should work fine here. This is with mypy 0.782 and on Python 3.6.
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
Reproduce the diagnostic with the a.py example from the issue by running mypy on it. Trace how attr.ib(converter=list) is interpreted for the annotated Sequence[str] attribute, then add coverage for this case and confirm that mypy no longer reports the incompatible list item error.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100