text: from django.db.models.query_utils import DeferredAttribute
  from django.forms.models import model_to_dict
  
  from ..backend import utils
  
  
  class UpdateScriptsMixin(object):
      pass
  
  
  class WooeyPy2Mixin(object):
      def __unicode__(self):
          return unicode(self.__str__())
  
  
  # from
  # http://stackoverflow.com/questions/1355150/django-when-saving-how-can-you-check-if-a-field-has-changed
  class ModelDiffMixin(object):
      """
      A model mixin that tracks model fields' values and provide some useful api
      to know what fields have been changed.
      """
  
      def __init__(self, *args, **kwargs):
          super(ModelDiffMixin, self).__init__(*args, **kwargs)
          self.__initial = self._dict
  
      @property
      def diff(self):
          d1 = self.__initial
          d2 = self._dict
          diffs = [(k, (v, d2[k])) for k, v in d1.items() if v != d2[k]]
          return dict(diffs)
  
      @property
      def has_changed(self):
          return bool(self.diff)
  
      @property
      def changed_fields(self):
          return self.diff.keys()
  
      def get_field_diff(self, field_name):
          """
          Returns a diff for field if it's changed and None otherwise.
          """
          return self.diff.get(field_name, None)
  
      def save(self, *args, **kwargs):
          """
          Saves model and set initial state.
          """
          super(ModelDiffMixin, self).save(*args, **kwargs)
          self.__initial = self._dict
  
      @property
      def _dict(self):
          exclude = self.get_deferred_fields()
          return model_to_dict(self, fields=[field.name for field in
                                             self._meta.fields], exclude=exclude)
  