Fix typechecking for async generators #17452
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
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Fixes #10534
This PR fixes a bug in typechecking asynchronous generators.
Mypy currently typechecks a generator/comprehension as
AsyncGeneratorif the leftmost expression containsawait, or if it contains anasync for.However, there are other situations where we should get async generator: If there is an
awaitexpression in any of the conditions or in any sequence except for the leftmost one, the generator/comprehension should also be typechecked asAsyncGenerator.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:
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.