Add explanations of the yield statement to common_issues.rst Fixes #17996 #18422
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sterliakov
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Jan 13, 2025
| def gen() -> Generator[int]: | ||
| ... # error: Missing return statement | ||
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| This kind of mistake is common in unfinished functions (the function body is ``...``). |
| Therefore, when using ``mypy`` to check types, we need to declare the return types | ||
| of such functions as Generator (or AsyncGenerator when the function is async). | ||
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| A common mistake is that we declared the return type of a function as |
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And this is wrong: "Missing return statement" is not specific to Generator, that's just because the return type is non-None and the body s trivial.
A reasonable function can return a Generator or Iterator and contain no yield (this passes):
from collections.abc import Generator
def fn() -> Generator[int]:
return (i for i in range(5))On the other hand, missing return statement causes a diagnostic without Generator too (except for stub files):
def fn() -> int:
... # E: Missing return statement [empty-body]There was a problem hiding this comment.
That sounds reasonable, I'll re-write these lines.
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Fixes #17996 @JelleZijlstra @hauntsaninja @tilboerner Please review :)
Add explanations of the yield statement to
common_issues.rst.No need for a test. Just modified the doc.