Allow `multiprocessing` Servers to return non-callables

Feature or enhancement

Proposal:

The logic for the multiprocessing Server class is the following for retrieving values from an instance referenced by a proxy:

https://github.com/python/cpython/blob/7d369d471cf2b067c4d795d70b75201c48b46f5b/Lib/multiprocessing/managers.py#L273-L286

It works well the majority of the time, but it fails when trying to get something that doesn't immediately return a callable (it can probably be a bit more specific when it comes to what type of callable it is). A change like the following would yield more robust behavior from a base point of view and wouldn't require reimplementation in a subclass:

value_or_function = getattr(obj, methodname, SENTINEL) 

if value_or_function is SENTINEL:
    raise AttributeError(f"Type '{obj.__class__.__name__}' has no attribute named '{methodname}'")

if isinstance(value_of_function, typing.Callable):  
    try: 
        res = value_or_function(*args, **kwds) 
    except Exception as e: 
        msg = ('#ERROR', e) 
    else: 
        typeid = gettypeid and gettypeid.get(methodname, None) 
        if typeid: 
            rident, rexposed = self.create(conn, typeid, res) 
            token = Token(typeid, self.address, rident) 
            msg = ('#PROXY', (rexposed, token)) 
        else: 
            msg = ('#RETURN', res)
else:
    msg = ('#RETURN', value_or_function)

There are likely edge cases that the above does not account for, but a change similar to the one above will open up the use of instance member variables and getters for properties.

A value for SENTINEL (or better) would obviously have to be defined somewhere (it's not in the example).

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Commencez dans Lib/multiprocessing/managers.py, au niveau de la logique de récupération de Server référencée dans l’issue. Suivez la manière dont l’accès aux attributs du proxy distingue les valeurs appelables des valeurs retournées, y compris le cas d’un attribut manquant et le chemin de création du proxy. Le travail est terminé lorsque les variables membres d’instance et les getters de propriétés peuvent être récupérés sans réimplémentation, tout en préservant le comportement existant des valeurs appelables.