title: How can I remove None elements from list of lists
body: <p>I have a list like this:</p>
  
  <pre><code>a = [[None, None, None],
       [None, None, None],
       [40.069, 18.642, 1.0],
       [41.18, 19.467, 1.0],
       [None, None, None]]
  </code></pre>
  
  <p>I want this to be like this. What is the best way to do this? Thanks </p>
  
  <pre><code>b = [[40.069, 18.642, 1.0], [41.18, 19.467, 1.0]]
  </code></pre>