Q:

planet+django makemigration does not work

I am trying to use django-planet on python 3, django 1.9.  After following the instruction on their page I get the following error after python manage.py makemigrations:

planet.Feed.site: (fields.E300) Field defines a relation with model
  'Site', whic h is either not installed, or is abstract.

A:

django-planet's author here :)
I've noticed, thanks to your question, that docs are missing an step: you have to add django.contrib.sitesto your settings.INSTALLED_APPS.
After that, please run ´python manage.py migrate´ since Django 1.9 adds one migration to make Site.domain field unique. 
I cant release yet a Django 1.9 compatible version for django-planet since django-tagging doesn't have an official release that supports it. But you can install the development version this way and your django-planet installation will work:
pip install -e git+git@github.com:Fantomas42/django-tagging.git@6246a1f270031908fe66cacbf1fb7a377021c4fc#egg=django-tagging

