EarlyStopping (keras) not working when placed inside a method

Question

EarlyStopping does not work when placed inside a method.

EarlyStopping does not work when running:

def model_training():
    # model, train_images, val_images, train_labels, val_images DEFINED HERE
    train_it = ImageDataGenerator().flow(train_images, y=train_labels, batch_size=32)
    val_it = ImageDataGenerator().flow(val_images, y=val_labels, batch_size=32)

    mc = ModelCheckpoint('model_name.h5', monitor='val_acc', save_best_only=True)

    es = EarlyStopping(monitor='val_loss', patience=1)

    history = model.fit_generator(
        train_it,
        steps_per_epoch=len(train_it),
        validation_data=val_it,
        validation_steps=len(val_it),
        epochs=50,
        callbacks=[es, mc],
    )
    _, acc = model.evaluate_generator(val_it, steps=len(val_it), verbose=1)


model_training()

EarlyStopping works when running:

# model, train_images, val_images, train_labels, val_images DEFINED HERE
train_it = ImageDataGenerator().flow(train_images, y=train_labels, batch_size=32)
val_it = ImageDataGenerator().flow(val_images, y=val_labels, batch_size=32)

mc = ModelCheckpoint('model_name.h5', monitor='val_acc', save_best_only=True)
es = EarlyStopping(monitor='val_loss', patience=1)

history = model.fit_generator(
    train_it,
    steps_per_epoch=len(train_it),
    validation_data=val_it,
    validation_steps=len(val_it),
    epochs=50,
    callbacks=[es, mc],
)
_, acc = model.evaluate_generator(val_it, steps=len(val_it), verbose=1)

Any idea why?

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UPDATE: EarlyStopping only working when patience=1.