Regression of os.scandir() typecheck
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bug
topic-type-variables
- Dominant language
- Python
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Description
Bug Report
Type variable inference related with os.scandir() seems to generate false-positives.
To Reproduce
Here is a minimal reproduction example, which is accepted by mypy 0.910 but rejected by 0.930 and 0.931.
from __future__ import annotations
import os
from pathlib import Path
def _calc_usage(target_path: Path | os.DirEntry) -> None:
with os.scandir(target_path) as scanner:
for entry in scanner:
if entry.is_dir():
_calc_usage(target_path)
else:
print('f')
_calc_usage(Path('.'))
Expected Behavior
Success: no issues found in 1 source file
Actual Behavior
test.py:8: error: Value of type variable "AnyStr" of "scandir" cannot be "Union[DirEntry[Any], Any]"
Your Environment
- Mypy version used: 0.931
- Mypy command-line flags:
python -m mypy test.py - Mypy configuration options from
mypy.ini(and other config files): - Python version used: 3.9.6
- Operating system and version: macOS 12.1
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 running the minimal reproduction in test.py with mypy 0.931 and compare it with 0.910. Trace the os.scandir() type-variable inference that produces the AnyStr error, and confirm the fix by rerunning the example with the expected successful result.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Clearly specified
- Newbie friendliness
- 42/100