src/transformers/trainer.py/Trainer/pop_callback
class Trainer:    def pop_callback(self, callback):
        """
        Remove a callback from the current list of [`~transformer.TrainerCallback`] and returns it.

        If the callback is not found, returns `None` (and no error is raised).

        Args:
           callback (`type` or [`~transformer.TrainerCallback`]):
               A [`~transformer.TrainerCallback`] class or an instance of a [`~transformer.TrainerCallback`]. In the
               first case, will pop the first member of that class found in the list of callbacks.

        Returns:
            [`~transformer.TrainerCallback`]: The callback removed, if found.
        """
        return self.callback_handler.pop_callback(callback)