gh-114104: clarify asynchronous comprehension docs to match runtime behavior #121175
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hauntsaninja
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Jun 30, 2024
Fixes #10534 This PR fixes a bug in typechecking asynchronous generators. Mypy currently typechecks a generator/comprehension as `AsyncGenerator` if the leftmost expression contains `await`, or if it contains an `async for`. However, there are other situations where we should get async generator: If there is an `await` expression in any of the conditions or in any sequence except for the leftmost one, the generator/comprehension should also be typechecked as `AsyncGenerator`. I've implemented this change in Mypy and added a test case to assert this behavior. If I enter the test cases into a regular repl, I can confirm that the runtime representation is generator/async_generator as the test case expects. According to the [language reference](https://docs.python.org/3/reference/expressions.html#grammar-token-python-grammar-comp_for): > If a comprehension contains either async for clauses or await expressions or other asynchronous comprehensions it is called an asynchronous comprehension. Confusingly, the documentation itself is actually not quite correct either, as pointed out in python/cpython#114104 Alongside this change, I've made a PR to update the docs to be more precise: python/cpython#121175 has more details.
hauntsaninja
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Jun 30, 2024
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Thanks for improving this and thanks for the mypy PR as well! |
Doc/reference/expressions.rst
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| :keyword:`!await` expressions anywhere except the iterable expression in the leftmost | ||
| :keyword:`!for` clause, or other asynchronous comprehensions, it is called an |
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"except the iterable expression in the leftmost :keyword:!for clause" is also applied to "other asynchronous comprehensions".
For example:
(x for x in foo(y async for y in a))Here the "for x" comprehension expression is not asynchronous.
kumaraditya303
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Jul 1, 2024
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Thanks @yangdanny97 for the PR, and @kumaraditya303 for merging it 🌮🎉.. I'm working now to backport this PR to: 3.12, 3.13. |
miss-islington
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Jul 1, 2024
…time behavior (pythonGH-121175) (cherry picked from commit 91313af) Co-authored-by: Danny Yang <yangdanny97@users.noreply.github.com>
miss-islington
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Jul 1, 2024
…time behavior (pythonGH-121175) (cherry picked from commit 91313af) Co-authored-by: Danny Yang <yangdanny97@users.noreply.github.com>
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GH-121234 is a backport of this pull request to the 3.13 branch. |
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GH-121235 is a backport of this pull request to the 3.12 branch. |
Akasurde
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Jul 3, 2024
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The documentation currently states:
According to the #114104,
awaitin the leftmost sequence of a comprehension does not make it an asynchronous comprehension, and the comments indicate that this is the intended behavior.This PR updates the documentation to reflect that.
awaitare compiled to async generators #114104📚 Documentation preview 📚: https://cpython-previews--121175.org.readthedocs.build/