Invalid import of OrderedDict from collections.abc

[kelvins]

OrderedDict should be imported from collections instead of collections.abc.

For example:

flask-restplus/flask_restplus/model.py

Lines 8 to 12 in 9232e1a

	try:
	from collections.abc import OrderedDict, MutableMapping
	except ImportError:
	# TODO Remove this to drop Python2 support
	from collections import OrderedDict, MutableMapping

When trying to import it gives the following error:

>>> from collections.abc import OrderedDict
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cannot import name 'OrderedDict' from 'collections.abc'

I have manually tested it on Python versions: 2.7, 3.4, 3.5, 3.6, 3.7 and 3.8.

The current code is not failing because of the try-except.

For tracking purposes, this change was made on PR #732 and is related to issue #727.

Can I submit a PR to solve this issue?

[Colin-b]

Indeed you are right, OrderedDict is not an abstract base class and is not within collections.abc as stated in python documentation. I can also submit a PR to fix my initial mistake.

[kelvins]

Thanks for the comment @Colin-b, I would like to submit a PR to solve this issue as my first contribution to the project, if you don't mind!? 😁