Remove traces of StrAndUnicode

This shift brings us closer to a Python3-first code base.

datatableview/compat.py

@@ -0,0 +1,19 @@
+""" Backports of code left behind by new versions of Django. """
+
+import six
+
+# Django 1.7 removed StrAndUnicode, so it has been purged from this project as well.  To bridge the
+# gap, we will rely on this utility directly, instead of trying to generate our own replacement
+# StrAndUnicode class.
+def python_2_unicode_compatible(klass):
+    """
+    A decorator that defines __unicode__ and __str__ methods under Python 2.
+    Under Python 3 it does nothing.
+
+    To support Python 2 and 3 with a single code base, define a __str__ method
+    returning text and apply this decorator to the class.
+    """
+    if not six.PY3:
+        klass.__unicode__ = klass.__str__
+        klass.__str__ = lambda self: self.__unicode__().encode('utf-8')
+    return klass

datatableview/utils.py

@@ -10,17 +10,12 @@
 
 from django.db.models.fields import FieldDoesNotExist
 from django.template.loader import render_to_string
+from django.forms.util import flatatt
 
 try:
-    from django.utils.encoding import StrAndUnicode
-except ImportError:
     from django.utils.encoding import python_2_unicode_compatible
-    @python_2_unicode_compatible
-    class StrAndUnicode:
-        def __str__(self):
-            return self.code
-
-from django.forms.util import flatatt
+except ImportError:
+    from .compat import python_2_unicode_compatible
 
 import six
 
@@ -155,7 +150,8 @@ def get_field_definition(field_definition):
     return FieldDefinitionTuple(*field)
 
 
-class DatatableStructure(StrAndUnicode):
+@python_2_unicode_compatible
+class DatatableStructure(object):
     """
     A class designed to be echoed directly to into template HTML to represent a skeleton table
     structure that datatables.js can use.
@@ -177,7 +173,7 @@ def __init__(self, ajax_url, options, model=None):
                 sort_direction = 'desc' if name[0] == '-' else 'asc'
                 self.ordering[plain_name] = ColumnOrderingTuple(i, index, sort_direction)
 
-    def __unicode__(self):
+    def __str__(self):
         return render_to_string(self.options['structure_template'], {
             'url': self.url,
             'result_counter_id': self.options['result_counter_id'],