BaseSerializer Implemented

[atb00ker]

Added new file openwisp_utils/api/serializers.py and implemented a base serializer that can be used in other projects.

Fixes #12

[coveralls]

Coverage increased (+0.5%) to 94.393% when pulling 29f7295 on atb00ker:issues/12_Shelf_Class into dc977d2 on openwisp:master.

[nemesifier]

@atb00ker great patch! I appreciate your effort to add the test 👍

Could you address my 2 comments below?

[nemesifier]

not all the packages using openwisp-utils have APIs and adding this here would make them download DRF even when not needed.

I suggest the following solution:

• remove this requirement here
• add djangorestframework>=3.8.2,<3.9 to requirements-test.txt
• add a try/except ImportError block when you import serializers in openwisp_utils/api/serializers.py, see my other comment

[nemesifier]

following the text of the other comment, here you could do something like:

try:
    from rest_framework import serializers
except ImportError:  # pragma: nocover
    import sys
    print('Django REST Framework is required to use this feature but it is not installed')
    sys.exit(1)

[atb00ker]

How about using django's abstraction for this?

from django.core.exceptions import ImproperlyConfigured

try:
    from rest_framework import serializers
except ImportError:  # pragma: nocover
    raise ImproperlyConfigured('Django REST Framework is required to use this feature but it is not installed')

[nemesifier]

sure, a lot better! 👍

[atb00ker]

Made the required changes. 😄

[nemesifier]

we usually break this kind of code into multiple lines with something like:

raise ImproperlyConfigured('Django REST Framework is required to use '
                           'this feature but it is not installed')

Could you update these 2 lines for consistency reasons please?

[nemesifier]

👍