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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Recent multiprocessing.Queue change breaks existing annotations and reduces typing precision","articleBody":"#4289 changed `multiprocessing.Queue` from a class to a function. This matches the implementation, but this has some possibly unanticipated side effects, as discussed in https://github.com/python/mypy/pull/9100. Here's a summary of the points raised in the linked PR:\r\n\r\n* `multiprocessing.Queue` is documented as a class: https://docs.python.org/3/library/multiprocessing.html#multiprocessing.Queue\r\n\r\n* `multiprocessing.queues.Queue` can be used in annotations, but it seems to be undocumented. For a user to annotate code using queues, they need to either read the stubs or the stdlib implementation, which is unfortunate.\r\n\r\n* The return type of `multiprocessing.Queue` is `Queue[Any]`, so the change loses some typing precision, even if a user can figure out the correct type. Since `multiprocessing.queues.Queue` is not very discoverable (as it's undocumented), for many new users this may effectively remove the ability to type check queue items.\r\n\r\n* The change breaks existing code that uses `multiprocessing.Queue` as a type, without an obvious fix.\r\n\r\nThe above considerations probably explain why `multiprocessing.Queue` used to be defined as a class, even thought it's not quite true.\r\n\r\nI'm not sure what's the best way forward. Here are some ideas:\r\n\r\n* Revert the change to `Queue` and other similar types (at least for now).\r\n* Teach type checkers to suggest using `multiprocessing.queues.Queue` (etc.) in type annotations. However, if these are undocumented, maybe we shouldn't recommend these?\r\n* Change the return type of `multiprocessing.Queue` to `Queue[T]` to preserve type checking precision (this may not work on all type checkers).","author":{"url":"https://github.com/JukkaL","@type":"Person","name":"JukkaL"},"datePublished":"2020-07-06T17:25:32.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/4313/typeshed/issues/4313"}