Make ralph working on Python 3.6

.travis.yml

@@ -35,7 +35,7 @@ cache:
 
 python:
     - "3.4"
-    # - "3.5"  # temporary removed to speedup build (python3.4 should be now used on production)
+    - "3.6"
 
 before_install:
     - pip install flake8==3.0.4 isort==4.2.5

requirements/base.txt

@@ -16,7 +16,7 @@ django-transaction-hooks==0.2  # it's merged to Django 1.9 - remove this when Dj
 djangorestframework==3.2.2
 djangorestframework_xml==1.2.0
 drf-nested-routers==0.11.1
-mysqlclient==1.3.6
+mysqlclient==1.3.13
 netaddr==0.7.18
 python-dateutil==2.4.2
 pytz==2015.4

src/ralph/data_importer/mixins.py

@@ -20,6 +20,8 @@ def __new__(cls, name, bases, attrs):
         Add additional fields to the export_class.fields with *_str
         for display ForeignKey fields.
         """
+        # https://bugs.python.org/issue29270
+        attrs.pop('__classcell__', None)
         new_class = super().__new__(cls, name, bases, attrs)
         # Generate second class only for export which has added
         # additional *_str fields