epochs = 500
batch_size = 256

model.fit_generator(datagen.flow(X_train, y_train, batch_size=batch_size, subset='training'),
                              steps_per_epoch=len(X_train) / 16, epochs=epochs,
                              callbacks=[checkpointer, stopper],
                              validation_data=datagen.flow(X_train, y_train,
                                                           batch_size=batch_size,
                                                           subset='validation'))

model_json = model.to_json()
with open("model.json", "w+") as json_file:
    json_file.write(model_json)