title: searching for a specific element in default dictionary PYTHOn
body: <p><strong>My dict:</strong></p>
  
  <pre><code>expiry_strike = defaultdict(&lt;type 'list'&gt;, {'2014-02-21': [122.5], '2014-01-24': [123.5, 122.5, 119.0, 123.0]})
  expiry_value = defaultdict(&lt;type 'list'&gt;, {'2014-02-21': [-100], '2014-01-24': [-200, 200, 1200, 200]})
  </code></pre>
  
  <p><strong>My question :</strong> </p>
  
  <p>I want to run a loop
  which finds the common element and in <code>expiry_strike</code> ( 122.5 in this case ),</p>
  
  <p>and if a common element is found, </p>
  
  <p>then I would like to add the values in <code>expiry_value</code> . ( here i want to add -100 + 200 ) </p>