我正在尝试学习TensorFlow并在以下位置研究示例： https : //github.com/aymericdamien/TensorFlow-Examples/blob/master/notebooks/3_NeuralNetworks/autoencoder.ipynb

然后，我在下面的代码中有一些疑问：

for epoch in range(training_epochs):
    # Loop over all batches
    for i in range(total_batch):
        batch_xs, batch_ys = mnist.train.next_batch(batch_size)
        # Run optimization op (backprop) and cost op (to get loss value)
        _, c = sess.run([optimizer, cost], feed_dict={X: batch_xs})
    # Display logs per epoch step
    if epoch % display_step == 0:
        print("Epoch:", '%04d' % (epoch+1),
              "cost=", "{:.9f}".format(c))

由于mnist只是一个数据集， mnist.train.next_batch到底是mnist.train.next_batch意思？如何定义dataset.train.next_batch ？

谢谢！