code: def get_value(self, obj):
          
          if self.attribute is None:
              return None
  
          attrs = self.attribute.split('__')
          value = obj
  
          for attr in attrs:
              try:
                  value = getattr(value, attr, None)
              except (ValueError, ObjectDoesNotExist):
                  # needs to have a primary key value before a many-to-many
                  # relationship can be used.
                  return None
              if value is None:
                  return None
  
          # RelatedManager and ManyRelatedManager classes are callable in
          # Django >= 1.7 but we don't want to call them
          if callable(value) and not isinstance(value, Manager):
              value = value()
          return value
docs: Returns the value of the object's attribute.