title: Combine 2 lists of pairs in Python
body: <p>I am trying to combine 2 lists of pairs.</p>
  
  <p><strong>List 1:</strong></p>
  
  
  
  <pre><code>dyndns = [('user1', 'dyndns1'), ('user2', 'dyddns2'), ('user3', 'dyndns3'), ('user4', 'dyddns4')]
  </code></pre>
  
  <p><strong>List 2:</strong></p>
  
  
  
  <pre><code>ip = [('user1', '1.1.1.1'), ('user2', '1.1.1.2'), ('user4', '1.1.1.4')]
  </code></pre>
  
  <p>I want to join List 1 to List 2, but only want to add the item from List 1 if it does not exist in List 2.<br>
  As you can see List 1 has user1, user2, user3 and user4, but List 2 only has user1, user2 and user4<br>
  The combined list has all users from List 2 as well as the extra users in List 1</p>
  
  <p><strong>Combined List:</strong></p>
  
  
  
  <pre><code>combined = [('user1', '1.1.1.1'), ('user2', '1.1.1.2'), ('user3', 'dyndns3'), ('user4', '1.1.1.4')]
  </code></pre>