title: How to use tf.data.Dataset and tf.keras do multi-inputs and multi-outpus?
body: <p>I meet one question about multi-output using tf.keras to build model and also using tf.data.Dataset as the input pipeline. Here is my code below:</p>
  
  <pre><code>  a = tf.keras.layers.Input(shape=(368, 368, 3))
    conv1 = tf.keras.layers.Conv2D(64, 3, 1)(a)
    conv2 = tf.keras.layers.Conv2D(64, 3, 1)(conv1)
    maxpool = tf.keras.layers.MaxPooling2D(pool_size=8, strides=8, 
     padding='same')(conv2)
    conv3 = tf.keras.layers.Conv2D(5, 1, 1)(maxpool)
    conv4 = tf.keras.layers.Conv2D(6, 1, 1)(maxpool)
  
    inputs = a
    outputs = [conv3, conv4]
  
    model = tf.keras.models.Model(inputs=inputs, outputs=outputs)
  
  
    model.compile(optimizer=tf.keras.optimizers.SGD(),
            loss=tf.keras.losses.mean_squared_error)
  
  
    import numpy as np
    data = np.random.rand(10, 368, 368, 3)
    cpm  = np.random.rand(10, 46, 46, 5)
    paf  = np.random.rand(10, 46, 46, 6)
  
    dataset1 = tf.data.Dataset.from_tensor_slices((data))
    dataset2 = tf.data.Dataset.from_tensor_slices((cpm, paf))
    dataset1 = dataset1.batch(10).repeat()
    dataset2 = dataset2.batch(10).repeat()
  
    dataset  = tf.data.Dataset.zip((dataset1, dataset2))
  
    model.fit(dataset, epochs=200, steps_per_epoch=30)
  </code></pre>
  
  <p>I'm using tensorflow==1.10.1 and I got error like this:</p>
  
  <pre><code> File "/home/ulsee/work/tensorflow-HalfBodyPose/learnkeras.py", line 123, in &lt;module&gt;
  model.fit(dataset, epochs=200, steps_per_epoch=30)
   File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/keras/engine/training.py", line 1278, in fit
  validation_split=validation_split)
   File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/keras/engine/training.py", line 917, in _standardize_user_data
  exception_prefix='target')
   File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/keras/engine/training_utils.py", line 143, in standardize_input_data
  data = [standardize_single_array(x) for x in data]
   File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/keras/engine/training_utils.py", line 143, in &lt;listcomp&gt;
  data = [standardize_single_array(x) for x in data]
   File "/usr/local/lib/python3.5/dist-packages/tensorflow/python/keras/engine/training_utils.py", line 81, in standardize_single_array
  elif x.ndim == 1:
  AttributeError: 'tuple' object has no attribute 'ndim'
  </code></pre>
  
  <p><strong>Update</strong> :
  I have made this code work after i upgrading tf==1.11.0. So maybe i think it's a version bug. </p>