--- description: Discover the essential base callbacks in Ultralytics for training, validation, prediction, and exporting models efficiently. keywords: Ultralytics, base callbacks, training, validation, prediction, model export, ML, machine learning, deep learning --- # Reference for `ultralytics/utils/callbacks/base.py` !!! Note This file is available at [https://github.com/ultralytics/ultralytics/blob/main/ultralytics/utils/callbacks/base.py](https://github.com/ultralytics/ultralytics/blob/main/ultralytics/utils/callbacks/base.py). If you spot a problem please help fix it by [contributing](https://docs.ultralytics.com/help/contributing/) a [Pull Request](https://github.com/ultralytics/ultralytics/edit/main/ultralytics/utils/callbacks/base.py) 🛠️. Thank you 🙏!

## ::: ultralytics.utils.callbacks.base.on_pretrain_routine_start

## ::: ultralytics.utils.callbacks.base.on_pretrain_routine_end

## ::: ultralytics.utils.callbacks.base.on_train_start

## ::: ultralytics.utils.callbacks.base.on_train_epoch_start

## ::: ultralytics.utils.callbacks.base.on_train_batch_start

## ::: ultralytics.utils.callbacks.base.optimizer_step

## ::: ultralytics.utils.callbacks.base.on_before_zero_grad

## ::: ultralytics.utils.callbacks.base.on_train_batch_end

## ::: ultralytics.utils.callbacks.base.on_train_epoch_end

## ::: ultralytics.utils.callbacks.base.on_fit_epoch_end

## ::: ultralytics.utils.callbacks.base.on_model_save

## ::: ultralytics.utils.callbacks.base.on_train_end

## ::: ultralytics.utils.callbacks.base.on_params_update

## ::: ultralytics.utils.callbacks.base.teardown

## ::: ultralytics.utils.callbacks.base.on_val_start

## ::: ultralytics.utils.callbacks.base.on_val_batch_start

## ::: ultralytics.utils.callbacks.base.on_val_batch_end

## ::: ultralytics.utils.callbacks.base.on_val_end

## ::: ultralytics.utils.callbacks.base.on_predict_start

## ::: ultralytics.utils.callbacks.base.on_predict_batch_start

## ::: ultralytics.utils.callbacks.base.on_predict_batch_end

## ::: ultralytics.utils.callbacks.base.on_predict_postprocess_end

## ::: ultralytics.utils.callbacks.base.on_predict_end

## ::: ultralytics.utils.callbacks.base.on_export_start

## ::: ultralytics.utils.callbacks.base.on_export_end

## ::: ultralytics.utils.callbacks.base.get_default_callbacks

## ::: ultralytics.utils.callbacks.base.add_integration_callbacks