Description

The changes made in 799ac4e added this import. In turn, this triggers the following DeprecationWarning from collections:

DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3, and in 3.9 it will stop working

The core python collections library has fully removed this functionality.

Proposed Fix

I believe that the correct solution is to change the imports from

from collections import deque, Callable

to

from collections import deque
from collections.abc import Callable