hvd_keras_fit.py

history = model.fit(train_dataset,
                    steps_per_epoch  = (NUM_TRAIN_IMAGES // batch_size) // size,
                    validation_data  = val_dataset,
                    validation_steps = (NUM_VALID_IMAGES // batch_size) // size,
                    verbose          = 1 if hvd.rank() == 0 else 0,
                    epochs           = epochs, callbacks=callbacks)