(🐞) `|` operator with `_SpecialForm` determined to be `types.UnionType` it's actually `typing.Union`
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bug
topic-pep-604
- Dominant language
- Python
- Stars
- 20.6k
- Forks
- 3.3k
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Description
from typing import Any
print(reveal_type(int | Any)) # types.UnionType
> python test.py
typing.Union[int, typing.Any]
This causes issues with isinstance, despite the fact that isinstance can take a typing.Union.
from typing import Any
isinstance(1, str | Any) # no error
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 Python snippets showing the mismatch between reveal_type(int | Any) and the runtime typing.Union result. Trace how mypy handles | when _SpecialForm is involved, then verify that the inferred type agrees with the runtime behavior and that the isinstance example remains error-free.
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
- 32/100