python里XGBClassifier怎么设置early stop？

early_stopping_rounds是在fit里设置，不是在XGBClassifier的初始化里

param_dist = {'objective':'binary:logistic', 'n_estimators':2}
clf = xgb.XGBClassifier(**param_dist)
clf.fit(X_train, y_train,
        eval_set=[(X_train, y_train), (X_test, y_test)],
        eval_metric='logloss',
        early_stopping_rounds=5,
        verbose=True)
evals_result = clf.evals_result()