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1. rafrafek

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Nov 15, 2022
2. AlexWaygood

   added

   topic-typing

   topic-multiprocessing

   on Nov 15, 2022
3. sobolevn

   added a commit that references this issue on Nov 15, 2022

   pythongh-99509: Add `__class_getitem__` to `multiprocessing.Qeueu`

   74dd0c8
4. JelleZijlstra

   added a commit that references this issue on Dec 27, 2022

   gh-99509: Add `__class_getitem__` to `multiprocessing.queues.Queue` (#…

   ...

   ce39aaf
5. JelleZijlstra

   closed this as completedon Dec 27, 2022
6. iritkatriel

   added a commit that references this issue on Dec 28, 2022

   Merged main into regmachine branch (#50)

   ...

   fdc73cb
7. linguini1 commented on Jun 15, 2023

   

   linguini1

   on Jun 15, 2023

   More actions

   I am using Python 3.11.4 and still get this error:

   from multiprocessing import Queue
   q: Queue[str] = Queue()

   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: 'method' object is not subscriptable
   

   And using

   import multiprocessing
   from multiprocessing.queues import Queue
   q: Queue[str] = multiprocessing.Queue()

   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: type 'Queue' is not subscriptable
   

   SimpleQueue subscripting only works when imported using from multiprocessing.queues import SimpleQueue.
8. Starbuck5 commented on Jul 10, 2023

   

   Starbuck5

   on Jul 10, 2023

   More actions

   I believe this should be re-opened.

   As reviewers noted in the linked PR, the linked PR only solves it for an undocumented way to import Queue. Also, even with the new import it's not a drop in replacement. I tested with 3.12beta 3.

   from multiprocessing.queues import Queue
   
   queue: Queue[str] = Queue()
   print(queue)

   The new import yields an error.

   Traceback (most recent call last):
     File "myfilelocation\test.py", line 3, in <module>
       queue: Queue[str] = Queue()
                           ^^^^^^^
   TypeError: Queue.__init__() missing 1 required keyword-only argument: 'ctx'
   

   To work around subscripting after this PR, you need to use the undocumented queue import and then provide this unknown context argument directly.

   from multiprocessing.queues import Queue
   import multiprocessing
   
   queue: Queue[str] = Queue(ctx=multiprocessing.get_context())
   print(queue)

   And of course the documented way of making a Queue still fails.

   from multiprocessing import Queue
   
   queue: Queue[str] = Queue()
   print(queue)

   Traceback (most recent call last):
     File "myfilelocation\test2.py", line 3, in <module>
       queue: Queue[str] = Queue()
              ~~~~~^^^^^
   TypeError: 'method' object is not subscriptable
   

   👍React with 👍3Reacted by Matteo Golin, hongwen000 and Simon H
9. hongwen000 commented on Oct 1, 2023

   

   hongwen000

   on Oct 1, 2023

   More actions

   @Starbuck5 Same issue
10. AlexWaygood commented on Oct 1, 2023

    

    AlexWaygood

    on Oct 1, 2023

    Member

    More actions

    To make both mypy and CPython happy, you can do something like this:

    import multiprocessing
    import multiprocessing.queues
    
    queue: multiprocessing.queues.Queue[str] = multiprocessing.Queue()

    This accurately reflects the facts that:

    1. multiprocessing.Queue() is the documented, public-API way of creating the class; however,
    2. multiprocessing.Queue itself is not a type (it's a method), so can't be used in a type annotation

    Could we special-case multiprocessing.Queue, perhaps by pretending in typeshed that it's a class rather than a method? Perhaps we could, but we like to avoid doing that kind of thing as much as possible. It's generally best for type checkers to be told the truth; lying to type checkers in typeshed about whether things are methods or classes can have unfortunate consequences. In any event, that conversation would probably need to take place on the https://github.com/python/typeshed/issues issue tracker rather than at CPython.

    Could multiprocessing.Queue itself be changed so that it's an actual class rather than a method? Again, perhaps. I'm not a multiprocessing expert, though (just a typing expert), so I can't really comment on that one.

    👍React with 👍6Reacted by YANG Qi, AndrewCleveland-Hearst, Shir Amir, Anton Yablokov, Jianan Wang and rysson