title: Get Keras input tensor from model
body: <p>I'm working through the Keras example for a sequence to sequence model.</p>
  
  <p><a href="https://github.com/keras-team/keras/blob/master/examples/lstm_seq2seq.py" rel="noreferrer">https://github.com/keras-team/keras/blob/master/examples/lstm_seq2seq.py</a></p>
  
  <p>In this example, they build a model from an input tensor.</p>
  
  <pre><code>encoder_inputs = Input(shape=(None, num_encoder_tokens))
  model = Model([encoder_inputs, decoder_inputs], decoder_outputs)
  print(encoder_inputs)
  </code></pre>
  
  <p>output:</p>
  
  <pre><code>Tensor("input_1:0", shape=(?, ?, 71), dtype=float32)
  </code></pre>
  
  <p>Once a model is built, is there a way to retrieve the input tensor from the model?  Something along the lines of </p>
  
  <pre><code>encoder_inputs = model.layers[0].??????
  </code></pre>