title: How to use tf.Dataset in Keras model.fit without specifying targets?
body: <p>I want to use an AutoEncoder model with Keras functional API. Also I want to use <code>tf.data.Dataset</code> as an input pipeline for the model. However, there is limitation that I can pass the dataset to the <code>keras.model.fit</code> only with tuple <code>(inputs, targets)</code> accroding to the <a href="https://www.tensorflow.org/api_docs/python/tf/keras/Model#fit" rel="nofollow noreferrer">docs</a>:</p>
  <blockquote>
  <p>Input data. It could be: A tf.data dataset. Should return a tuple of either (inputs, targets) or (inputs, targets, sample_weights).</p>
  </blockquote>
  <p>So here is the question: can I pass the <code>tf.data.Dataset</code> without repeating inputs like that <code>(inputs, inputs)</code> and more like <code>(inputs, None)</code>. And if I can't, will the repeated inputs double the GPU memory for my model?</p>