Convert dict fields into objects, where appropriate

def _update_fields_with_objects(self):
        """ Convert dict fields into objects, where appropriate """
        # Update the photo target with photo objects
        if self.target is not None:
            if self.target_type == "photo":
                self.target = Photo(self._client, self.target)
            else:
                raise NotImplementedError("Actions can only be assigned to "
                                          "Photos")