title: Pandas select columns using list but ignore missing column names
body: <p>I have a dataframe</p>
  
  <pre><code>    'A'   'B'   'C'   'X'   ,'Y'    ,  'Z'
  0   
  1
  2
  3
  4
  5
  </code></pre>
  
  <p>and a list <code>l=[A,B,C,D,E,F]</code></p>
  
  <p>I want to use that that list to select columns that are in the list but ignore the ones that don't appear.</p>
  
  <p>So the expected output is </p>
  
  <pre><code>  'A'   'B'   'C'  
  0   
  1
  2
  3
  4
  5
  </code></pre>