Use zip as izip on Python 3
Use explicit relative imports

Run python-modernize with imports fixer
Use BytesIO for cStringIO
Cutting out circular imports as far as possible
div operator is gone on Python 3
Define basestring for Python 3
Define iteritems for Python 3
next() method to function
Renamed assertion method in Py3
Use basestring in dataset
Print function in tests
Pickle import fallback
Define xrange for Python 3
Use iteritems and itervalues functions in tests
Fix uses of keys that want lists
Alias assertItemsEqual for Py3
Define and use unicode_type
Relative import in tests
Use reduce from functools
Fix one test