Why is the Callable ABC in the collections ABC module?

Question

The Python collections.abc module contains many handy ABCs for checking various features of objects, but one that doesn't appear to belong is Callable. No standard collection is callable, and PEP 3119 doesn't provide any reasoning or even mention the Callable ABC, so why is it in this package instead of somewhere else?

Context: I'm writing a Python->Java compiler for fun, and I just wanted to see if there was any reasoning behind the decision so I could list that reasoning in my code.

Answer 1

The module originates from PEP-3119 which proposes:

Specific ABCs for containers and iterators, to be added to the collections module.

But since then, it evolved to be something more. And now a module description does not mention containters and iterators explictly. It says:

This module provides abstract base classes that can be used to test whether a class provides a particular interface; for example, whether it is hashable or whether it is a mapping.

I believe it is a collections submodule just because it was a part of it in the past:

New in version 3.3: Formerly, this module was part of the collections module.