title: ValueError compatibility and multi-line string aesthetics?
body: <p>I am trying to write a ValueError message in a nice compact, and clean looking way: </p>
  
  <pre><code>    raise ValueError("Model Architecture Not Recognized. Please ensure that your model's filename contains either"
      """ "vgg" and "16" for a 16 layer VGG model, "vgg" and "19" for a 19 layer VGG model, or "nin" for a Network"""
      " In Network model. Note that filenames are not case sensitive.")   
  </code></pre>
  
  <p>Will this work for both Python 2.7 and Python 3? Is there a better way to have a multi-line error message? Are there any issues with not using a <code>+</code> in between the strings used for the error message? </p>