如何在Keras模型中使用F1评分？

from keras import backend as K
from sklearn.metrics import f1_score

def f1(y_true, y_pred):
    y_pred = K.round(y_pred)
    return f1_score(y_true, y_pred)

model.compile(optimizer='adam', loss='binary_crossentropy', metrics=['accuracy', f1])

class F1ScoreCallback(keras.callbacks.Callback):
    def on_epoch_end(self, epoch, logs={}):
        val_f1 = logs.get('val_f1')
        print("val_f1: {:.4f}".format(val_f1))

model.fit(X_train, y_train, validation_data=(X_val, y_val), callbacks=[F1ScoreCallback()])