title: Name of input and output tensors when loading Keras model to TensorFlow
body: <p>I'm trying to use Keras' model in "pure" TensorFlow (I want to use it in Android app). I've successfully exported Keras model to protobuf and imported it to Tensorflow. However running tensorflow model requires providing input and output tensors' names and I don't know how to find them. My model looks like this:</p>
  
  <pre><code>seq = Sequential()
  seq.add(Convolution2D(32, 3, 3, input_shape=(3, 15, 15), name="Conv1"))
  ....
  seq.add(Activation('softmax', name="Act4"))
  seq.compile()
  </code></pre>
  
  <p>When I'm printing tensors in TensorFlow I can find:</p>
  
  <pre><code>Tensor("Conv1_W/initial_value:0", shape=(32, 3, 3, 3), dtype=float32)
  Tensor("Conv1_W:0", dtype=float32_ref)
  Tensor("Conv1_W/Assign:0", shape=(32, 3, 3, 3), dtype=float32_ref)
  Tensor("Conv1_W/read:0", dtype=float32)
  
  Tensor("Act4_sample_weights:0", dtype=float32)
  Tensor("Act4_target:0", dtype=float32)
  </code></pre>
  
  <p>Hovewer, there are no tensors that have shape (3,15,15).</p>
  
  <p>I've seen <a href="https://blog.keras.io/keras-as-a-simplified-interface-to-tensorflow-tutorial.html" rel="noreferrer">here</a> that I can add "my_input_tensor" as input, hovewer I don't know which type is it - I've tried TensorFlow's and Keras' placeholders and they gave me this error:</p>
  
  <pre><code>/XXXXXXXXX/lib/python2.7/site-packages/keras/engine/topology.pyc in __init__(self, input, output, name)
     1599             # check that x is an input tensor
     1600             layer, node_index, tensor_index = x._keras_history
  -&gt; 1601             if len(layer.inbound_nodes) &gt; 1 or (layer.inbound_nodes and layer.inbound_nodes[0].inbound_layers):
     1602                 cls_name = self.__class__.__name__
     1603                 warnings.warn(cls_name + ' inputs must come from '
  
  AttributeError: 'NoneType' object has no attribute 'inbound_nodes'
  </code></pre>