Return type "str" of "readline" incompatible with return type "bytes" in supertype "IOBase" [override]
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bug
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Description
Since https://github.com/python/typeshed/pull/4145 (released with mypy 0.790) mypy fails with:
import io
class MyStringIO(io.StringIO):
def readline(self, size=None) -> str:
return super().readline(size)
Return type "str" of "readline" incompatible with return type "bytes" in supertype "IOBase" [override]
According to https://github.com/python/typeshed/pull/4145#issuecomment-639543492 this is likely a bug in mypy.
(mypy 0.800+dev.f220ce50725ed7f117832b9f03aed4d1a9508e00 (current master))
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
Run the supplied StringIO reproducer with mypy and investigate override checking for io.StringIO.readline against IOBase. Add regression coverage for the reported error and verify that the override is accepted without introducing related type-checking regressions.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100