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description: Explore how to use the on-train, on-validation, on-pretrain, and on-predict callbacks in Ultralytics. Learn to update params, save models, and add integration callbacks.
keywords: Ultralytics, Callbacks, On-train, On-validation, On-pretrain, On-predict, Parameters update, Model saving, Integration callbacks
---

# 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 🙏!

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## ::: ultralytics.utils.callbacks.base.on_pretrain_routine_start
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## ::: ultralytics.utils.callbacks.base.on_pretrain_routine_end
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## ::: ultralytics.utils.callbacks.base.on_train_start
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## ::: ultralytics.utils.callbacks.base.on_train_epoch_start
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## ::: ultralytics.utils.callbacks.base.on_train_batch_start
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## ::: ultralytics.utils.callbacks.base.optimizer_step
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## ::: ultralytics.utils.callbacks.base.on_before_zero_grad
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## ::: ultralytics.utils.callbacks.base.on_train_batch_end
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## ::: ultralytics.utils.callbacks.base.on_train_epoch_end
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## ::: ultralytics.utils.callbacks.base.on_fit_epoch_end
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## ::: ultralytics.utils.callbacks.base.on_model_save
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## ::: ultralytics.utils.callbacks.base.on_train_end
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## ::: ultralytics.utils.callbacks.base.on_params_update
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## ::: ultralytics.utils.callbacks.base.teardown
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## ::: ultralytics.utils.callbacks.base.on_val_start
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## ::: ultralytics.utils.callbacks.base.on_val_batch_start
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## ::: ultralytics.utils.callbacks.base.on_val_batch_end
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## ::: ultralytics.utils.callbacks.base.on_val_end
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## ::: ultralytics.utils.callbacks.base.on_predict_start
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## ::: ultralytics.utils.callbacks.base.on_predict_batch_start
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## ::: ultralytics.utils.callbacks.base.on_predict_batch_end
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## ::: ultralytics.utils.callbacks.base.on_predict_postprocess_end
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## ::: ultralytics.utils.callbacks.base.on_predict_end
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## ::: ultralytics.utils.callbacks.base.on_export_start
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## ::: ultralytics.utils.callbacks.base.on_export_end
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## ::: ultralytics.utils.callbacks.base.get_default_callbacks
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## ::: ultralytics.utils.callbacks.base.add_integration_callbacks
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