title: Remove duplicated tuples from list based on the first entry of tuple
body: <p>I have a list of tuples like this one here:</p>
  
  <pre><code>test = [('ent1', 24), ('ent2',12), ('ent3',4.5), ('ent1', 4), ('ent2', 3.5)]
  </code></pre>
  
  <p>I would like to remove those tuples from the list where the first element has already appeared. So the desired output would be</p>
  
  <pre><code>[('ent1', 24), ('ent2',12), ('ent3',4.5)]
  </code></pre>
  
  <p>I have no idea how to do this. Normally, if I would like to remove exact duplicated tuples, I would use</p>
  
  <pre><code>list(set(test))
  </code></pre>
  
  <p>but this is not working in this case. Has anybody an appropriate approach for this problem?</p>