.. testsetup:: *

    from pytorch_lightning.trainer.trainer import Trainer
    from pytorch_lightning.callbacks.early_stopping import EarlyStopping


Early stopping
==============

Stopping an epoch early
-----------------------
You can stop an epoch early by overriding :meth:`~pytorch_lightning.core.lightning.LightningModule.on_batch_start` to return `-1` when some condition is met.

If you do this repeatedly, for every epoch you had originally requested, then this will stop your entire run.

Default Epoch End Callback Behavior
-----------------------------------
By default early stopping will be enabled if `'val_loss'`
is found in :meth:`~pytorch_lightning.core.lightning.LightningModule.validation_epoch_end`'s
return dict. Otherwise training will proceed with early stopping disabled.

Enable Early Stopping using Callbacks on epoch end
--------------------------------------------------
There are two ways to enable early stopping using callbacks on epoch end.

-   Set early_stop_callback to True. Will look for 'val_loss' in validation_epoch_end() return dict.
    If it is not found an error is raised.

    .. testcode::

        trainer = Trainer(early_stop_callback=True)

-   Or configure your own callback

    .. testcode::

        early_stop_callback = EarlyStopping(
            monitor='val_loss',
            min_delta=0.00,
            patience=3,
            verbose=False,
            mode='min'
        )
        trainer = Trainer(early_stop_callback=early_stop_callback)

In any case, the callback will fall back to the training metrics (returned in
:meth:`~pytorch_lightning.core.lightning.LightningModule.training_step`,
:meth:`~pytorch_lightning.core.lightning.LightningModule.training_step_end`)
looking for a key to monitor if validation is disabled or
:meth:`~pytorch_lightning.core.lightning.LightningModule.validation_epoch_end`
is not defined.

.. seealso::
    - :class:`~pytorch_lightning.trainer.trainer.Trainer`
    - :class:`~pytorch_lightning.callbacks.early_stopping.EarlyStopping`

Disable Early Stopping with callbacks on epoch end
--------------------------------------------------
To disable early stopping pass ``False`` to the
:paramref:`~pytorch_lightning.trainer.trainer.Trainer.early_stop_callback`.
Note that ``None`` will not disable early stopping but will lead to the
default behaviour.

.. seealso::
    - :class:`~pytorch_lightning.trainer.trainer.Trainer`
    - :class:`~pytorch_lightning.callbacks.early_stopping.EarlyStopping`