title: Python function list parameter variable structure
body: <p>I'm having trouble using the function below. I'm unable to figure out the <code>routes</code> parameter structure.</p>
  
  <pre><code>def show_image(data, routes=[]):
      '''
      Given a list of lists of integers "data",
      and an optional list of boolean list of lists "routes",
      show the data as an image and overlay the routes on the image in red.
      '''
      image_data = [x[:] for x in data]
      for i in range(len(image_data)):
          for j in range(len(image_data[i])):
              image_data[i][j] = [image_data[i][j]] * 3
              if any(route[i][j] for route in routes):
                  image_data[i][j] = [255, 0, 0]
      io.imshow(np.array(image_data, dtype=np.uint8))
      io.show()
  
  </code></pre>
  
  <p>I have data parameter working, but I'm unsure about <code>routes = []</code>. I know it takes a <code>"list of boolean list of lists"</code> which im assuming to be something like this:</p>
  
  <pre><code>[[True, True], [False,False]]
  </code></pre>
  
  <p>Can someone give me some dummy <code>data</code> parameter to put in to see how it works? Thanks</p>