narrowed variable does not work when used as default value
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bug
- Dominant language
- Python
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Description
value: int | None = 1
if value:
reveal_type(value) # int (correct)
def foo(a: int = value): # int | None (incorrect)
reveal_type(value) # int | None (correct)
since default values are only evaluated once when the function is defined, it should be narrowed here
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First steps
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- Open a pull request that references the issue number.
Research direction
Start with the linked mypy-play reproduction and trace how narrowed types are handled when an expression is used as a function default value. Done means the default argument a: int = value is accepted after the narrowing, while reveal_type(value) inside foo remains int | None.
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
- Mostly clear
- Newbie friendliness
- 35/100