title: best way to get right thing using python
body: <p>this is my code :</p>
  
  <pre><code>a=[{'x':'aaa','b':'bbbb'},{'x':'a!!!','b':'b!!!'},{'x':'2222','b':'dddd'},{'x':'ddwqd','b':'dwqd'}]
  </code></pre>
  
  <p>and i want get every 'x' list like this :</p>
  
  <pre><code>['aaa','a!!!','2222','ddwqd']
  </code></pre>
  
  <p>so which is the best way to get this ,</p>
  
  <p>use map ??</p>
  
  <p>thanks</p>