title: Add item to list if not already exists
body: <p>I'm new to Python and got following problem:</p>
  
  <pre><code>a = [[0,abc,1],[0,def,1]]
  
  b = [abc,jkl]
  </code></pre>
  
  <p>Output should be:</p>
  
  <pre><code>c = [[0,abc,1],[0,def,1],[0,jkl,1]]
  </code></pre>
  
  <p>Can anyone help me out there?</p>