code: def model_delta(old_model, new_model):
      
  
      delta = {}
      fields = new_model._meta.fields
      for field in fields:
          old_value = get_field_value(old_model, field)
          new_value = get_field_value(new_model, field)
          if old_value != new_value:
              delta[field.name] = [smart_text(old_value),
                                   smart_text(new_value)]
  
      if len(delta) == 0:
          delta = None
  
      return delta
docs: Provides delta/difference between two models
      :param old: The old state of the model instance.
      :type old: Model
      :param new: The new state of the model instance.
      :type new: Model
      :return: A dictionary with the names of the changed fields as keys and a
               two tuple of the old and new field values
               as value.
      :rtype: dict