This pull request registers array.array to collections.abc.MutableSequence._abc_registry and it makes isinstance(array.array("<type>"), collections.abc.MutableSequence) as true.

There is an issue that it cannot load MutableSequence from collections.abc, so I bypassed it by loading MutableSequence from _collections_abc directly. But it should be fixed or note comments about specific reason.

You can run the below code to test these changes:

import array, collections.abc; print(isinstance(array.array('B'), collections.abc.MutableSequence))

Related links

• https://github.com/python/cpython/blob/bd7903967cd2a19ebc842dd1cce75f60a18aef02/Modules/arraymodule.c#L3075-L3088