src/transformers/utils/notebook.py/NotebookProgressCallback/on_train_begin
class NotebookProgressCallback:    def on_train_begin(self, args, state, control, **kwargs):
        self.first_column = "Epoch" if args.evaluation_strategy == IntervalStrategy.EPOCH else "Step"
        self.training_loss = 0
        self.last_log = 0
        column_names = [self.first_column] + ["Training Loss"]
        if args.evaluation_strategy != IntervalStrategy.NO:
            column_names.append("Validation Loss")
        self.training_tracker = NotebookTrainingTracker(state.max_steps, column_names)