old_contents: from south.modelsinspector import add_introspection_rules
  
  try:
      from tagging.fields import TagField
  except ImportError:
      pass
  else:
      rules = [
          (
              (TagField, ),
              [],
              {
                  "blank": ["blank", {"default": True}],
                  "max_length": ["max_length", {"default": 255}],
              },
          ),
      ]
  
      add_introspection_rules(rules, ["^tagging\.fields",])
  
new_contents: from south.modelsinspector import add_introspection_rules
  from django.conf import settings
  
  if "tagging" in settings.INSTALLED_APPS:
      try:
          from tagging.fields import TagField
      except ImportError:
          pass
      else:
          rules = [
              (
                  (TagField, ),
                  [],
                  {
                      "blank": ["blank", {"default": True}],
                      "max_length": ["max_length", {"default": 255}],
                  },
              ),
          ]
      
          add_introspection_rules(rules, ["^tagging\.fields",])
  
subject: Fix #457