title: Keras TypeError: fit() missing 1 required positional argument: 'y'
body: <p>My model is correctly formed:</p>
  
  <pre><code>model = Sequential()
  model.add(Lambda(lambda x:x/255.0 - 0.5, input_shape=(160,320,3)))
  model.compile(loss='mse', optimizer='adam')
  model.fit(train_generator, samples_per_epoch= len(train_samples), validation_data=validation_generator, nb_val_samples=len(validation_samples), nb_epoch=3)
  </code></pre>
  
  <p>Note, parenthesis are in place.  However when I fit I get the following error:</p>
  
  <pre><code>Traceback (most recent call last):   File "modell.py", line 70, in &lt;module&gt;
      model.fit(train_generator, samples_per_epoch= len(train_samples), validation_data=validation_generator, nb_val_samples=len(validation_samples), nb_epoch=3) 
  TypeError: fit() missing 1 required positional argument: 'y'
  </code></pre>
  
  <p><code>train_generator</code> is a 2D array </p>
  
  <pre><code>train_generator = generator(train_samples, batch_size=32)
  </code></pre>
  
  <p>I must be blind because I can't spot the problem. Does anyone know why <code>fit</code> is looking for an extra argument?  </p>