Improve yield from inference for unions of generators #16717
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New error in rich is a true positive |
| # Supertype of Generator (Iterator, Iterable, object): tr is any. | ||
| return AnyType(TypeOfAny.special_form) | ||
| # We have a supertype of Generator (Iterator, Iterable, object) | ||
| # Treat `Iterator[X]` as a shorthand for `Generator[X, Any, None]`. |
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Why? Intuitively Any makes more sense to me here.
This affects code like this, right?
x: Iterator[T]
y = yield from xThere was a problem hiding this comment.
This allows us to produce errors for cases like python/typeshed#11222 / testReturnInIterator
test-data/unit/check-statements.test
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| class T: pass | ||
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| def foo(arg: Union[Generator[int, None, T], Iterable[str]]) -> Generator[Union[int, str], None, Optional[T]]: |
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This is unsound and should arguably error. For example, I could pass a Generator[str, None, str] and get a different type out.
Possibly we should allow it for pragmatic reasons, but then again I'm not sure how often people use yield from with values typed as just Iterable.
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Oh this is a great point. I've added a test, but I think this is pre-existing, Iterable[str] acts like Generator[str, Any, Any] in argument positions. mypy handles generator returns kind of weirdly, like it thinks the type of the yield from expr is the return type
mypy's existing behaviour is to error with Function does not return a value (it only ever returns None) [func-returns-value] on the return statement, which doesn't make sense to me
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Diff from mypy_primer, showing the effect of this PR on open source code: rich (https://github.com/Textualize/rich)
+ rich/segment.py:607: error: No return value expected [return-value]
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Fixes #15141, closes #15168