How to use collections.abc from both Python 3.8+ and Python 2.7

Question

In Python 3.3 "abstract base classes" in collections (like MutableMapping or MutableSequence) were moved to second-level module collections.abc. So in Python 3.3+ the real type is collections.abc.MutableMapping and so on. Documentation states that the old alias names (e.g. collections.MutableMapping) will be available up to Python 3.7 (currently the latest version), however in 3.8 these aliases will be removed.

Current version of Python 3.7 even produces a warning when you use the alias names:

./scripts/generateBoard.py:145: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working   elif isinstance(value, (collections.MutableMapping, collections.MutableSequence)) == True: 

In python 2.7 there is no collections.abc.

How can Python script handle this difference in the most convenient way, when it is meant to be used with (almost) any Python version? I'm looking for a solution which would ideally solve this mess in one central place, without having to use try: ... except: ... all over the script everywhere I need this type?

Answer 1

Place this at the top of the script:

import collections  try:     collectionsAbc = collections.abc except AttributeError:     collectionsAbc = collections 

Then change all prefixes of the abstract base types, e.g. change collections.abc.MutableMapping or collections.MutableMapping to collectionsAbc.MutableMapping.

Alternatively, import what you require in the script at the top in a single place:

try:     from collections.abc import Callable  # noqa except ImportError:     from collections import Callable  # noqa