Make standard container classes satisfy container Protocols.

[randolf-scholz]

🚀 The feature, motivation and pitch

The container classes in torch/nn/modules/container satisfy the necessary methods to use corresponding collections.abc Mixins, I propose to either subclass these, or to satisfy the protocols manually:

• nn.Sequential -> MutableSequence[M]
• nn.ModuleList -> MutableSequence[M]
• nn.ModuelDict -> MutableMapping[str, M]
• nn.ParameterList -> Sequence[P] (missing: __delitem__ and insert for MutableSequence[M])
• nn.ParameterDict -> MutableMapping[str, P]
• M would be a TypeVar bound to nn.Module.
• P would be a TypeVar bound to nn.Parameter.

Alternatives

No response

Additional context

No response

cc @albanD @mruberry @jbschlosser @walterddr @mikaylagawarecki

[mikaylagawarecki]

Related to #80821

[mikaylagawarecki]

It seems like something similar was tried previously in #89135 (comment), but this ended up changing the metaclass nn.ModuleList, which was BC-breaking, see the linked comment for an example of a situation where this was BC-breaking.

I tried this locally as well to verify and got before

>>> print(type(torch.nn.ModuleList))
<class 'type'>

after:

>>> print(type(torch.nn.ModuleList))
<class 'abc.ABCMeta'>

Could you share more details about why satisfying container Protocols would be helpful? Additionally, do you have ideas for how to prevent the BC-break?