Hmm... I suppose one reason for not making these subscriptable at runtime might be that these are undocumented classes that aren't included in __all__. But I personally still lean towards making them subscriptable, nonetheless.

Maybe these classes should be documented? I'm also a bit hesitant about this if these classes are undocumented.

Maybe these classes should be documented? I'm also a bit hesitant about this if these classes are undocumented.

@gpshead, any thoughts from you on this, as a multiprocessing expert? I think there's a decent case for documenting these classes, since instances of ListProxy and DictProxy are returned from multiprocessing.managers.SyncManager.list() and multiprocessing.managers.SyncManager.dict() respectively. Both of those are public, documented methods:

• https://docs.python.org/3/library/multiprocessing.html#multiprocessing.managers.SyncManager.list
• https://docs.python.org/3/library/multiprocessing.html#multiprocessing.managers.SyncManager.dict

@JelleZijlstra: What do you think?

@gvanrossum, @carljm (typing experts): Do you want to review this typing change?

@vstinner, this needs input from multiprocessing experts, not typing experts. Two typing experts have already given their input here (Jelle and myself). From a typing perspective, the change is fine. But from a multiprocessing perspective: the classes are currently undocumented and not included in __all__. Adding __class_getitem__ might encourage their use in type annotations. Is that okay? Should we document these classes, or are they best left undocumented? What's our position on that?

@pitrou: Do you have an opinion on this change?

I don't think anyone wants to claim expertise for multiprocessing no matter how much we've done work on it. This change looks good to me, I made a couple edits.

I have no idea what a GenericAlias is, and the doc is rather cryptic. As long as this doesn't change runtime behavior I see no reason to oppose it.

Thanks for making _BaseDictProxy private.