Allow to dispatch getting documentation on objects.

[Carreau]

Base for #13860, so that object can be queried for documentation on their fields/properties.

Typically this allows the following, to extend the doc documentation when requesting information on a field.

class DictLike:
    def __getitem__(self, k):
        if k.startswith('f'):
            return "documentation for k"
        else:
            raise KeyError

class Bar:
    __custom_documentations__ = DictLike()

    faz = 1


    @property
    def foo(self):
        return 1
b = Bar()
b.faz?

[krassowski]

I guess I am late to notice this, but should we also allow __custom_documentation__ (no s) since in common usage documentation is uncountable? Any native speakers with an opinion?

[Carreau]

I guess I am late to notice this, but should we also allow __custom_documentation__ (no s) since in common usage documentation is uncountable? Any native speakers with an opinion?

Sorry I havent' responded to that.

For me __custom_documentation__ would be a single string not a container of string.