Reference for ultralytics/utils/callbacks/platform.py

def on_pretrain_routine_start(trainer):
    """Initialize and start console logging immediately at the very beginning."""
    if RANK in {-1, 0}:
        from ultralytics.utils.logger import DEFAULT_LOG_PATH, ConsoleLogger, SystemLogger

        trainer.system_logger = SystemLogger()
        trainer.console_logger = ConsoleLogger(DEFAULT_LOG_PATH)
        trainer.console_logger.start_capture()

def on_pretrain_routine_end(trainer):
    """Handle pre-training routine completion event."""
    pass

def on_fit_epoch_end(trainer):
    """Handle end of training epoch event and collect system metrics."""
    if RANK in {-1, 0} and hasattr(trainer, "system_logger"):
        system_metrics = trainer.system_logger.get_metrics()
        print(system_metrics)  # for debug

def on_model_save(trainer):
    """Handle model checkpoint save event."""
    pass

def on_train_end(trainer):
    """Stop console capture and finalize logs."""
    if logger := getattr(trainer, "console_logger", None):
        logger.stop_capture()

def on_train_start(trainer):
    """Handle training start event."""
    pass

def on_val_start(validator):
    """Handle validation start event."""
    pass

def on_predict_start(predictor):
    """Handle prediction start event."""
    pass

def on_export_start(exporter):
    """Handle model export start event."""
    pass