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##################
Callback Functions
##################
This document gives a basic walkthrough of :ref:`callback API <callback_api>` used in
XGBoost Python package. In XGBoost 1.3, a new callback interface is designed for Python
package, which provides the flexibility of designing various extension for training.
Also, XGBoost has a number of pre-defined callbacks for supporting early stopping,
checkpoints etc.
Using builtin callbacks
-----------------------
By default, training methods in XGBoost have parameters like ``early_stopping_rounds`` and
``verbose``/``verbose_eval``, when specified the training procedure will define the
corresponding callbacks internally. For example, when ``early_stopping_rounds`` is
specified, :py:class:`EarlyStopping <xgboost.callback.EarlyStopping>` callback is invoked
inside iteration loop. You can also pass this callback function directly into XGBoost:
.. code-block:: python
D_train = xgb.DMatrix(X_train, y_train)
D_valid = xgb.DMatrix(X_valid, y_valid)
# Define a custom evaluation metric used for early stopping.
def eval_error_metric(predt, dtrain: xgb.DMatrix):
label = dtrain.get_label()
r = np.zeros(predt.shape)
gt = predt > 0.5
r[gt] = 1 - label[gt]
le = predt <= 0.5
r[le] = label[le]
return 'CustomErr', np.sum(r)
# Specify which dataset and which metric should be used for early stopping.
early_stop = xgb.callback.EarlyStopping(rounds=early_stopping_rounds,
metric_name='CustomErr',
data_name='Valid')
booster = xgb.train(
{'objective': 'binary:logistic',
'eval_metric': ['error', 'rmse'],
'tree_method': 'hist'}, D_train,
evals=[(D_train, 'Train'), (D_valid, 'Valid')],
feval=eval_error_metric,
num_boost_round=1000,
callbacks=[early_stop],
verbose_eval=False)
dump = booster.get_dump(dump_format='json')
assert len(early_stop.stopping_history['Valid']['CustomErr']) == len(dump)
Defining your own callback
--------------------------
XGBoost provides an callback interface class: :py:class:`TrainingCallback
<xgboost.callback.TrainingCallback>`, user defined callbacks should inherit this class and
override corresponding methods. There's a working example in
:ref:`sphx_glr_python_examples_callbacks.py`.
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