title: Extracting dictionary items embedded in a list
body: <p>Let's say I have the following list of dict</p>
  
  <pre><code>t = [{'a': 1.0, 'b': 2.0},
       {'a': 3.0, 'b': 4.0},
       {'a': 5.0, 'b': 6.0},
       {'a': 7.0, 'b': 9.0},
       {'a': 9.0, 'b': 0.0}]
  </code></pre>
  
  <p>Is there an efficient way to extract all the values contained in the dictionaries with a dictionary key value of <code>a</code>?</p>
  
  <p>So far I have come up with the following solution</p>
  
  <pre><code>x = []
  for j in t:
      x.append(j['a'])
  </code></pre>
  
  <p>However, I don't like to loop over items, and was looking at a nicer way to achieve this goal.</p>