code: def has_changed(self, field):
          
          if field in self.fields:
              # deferred fields haven't changed
              if field in self.deferred_fields and field not in self.instance.__dict__:
                  return False
              return self.previous(field) != self.get_field_value(field)
          else:
              raise FieldError('field "%s" not tracked' % field)
docs: Returns ``True`` if field has changed from currently saved value