title: Find out if no items in a list are keys in a dictionary
body: <p>I have this list:</p>
  
  <pre><code>source = ['sourceid', 'SubSourcePontiflex', 'acq_source', 'OptInSource', 'source',
        'SourceID', 'Sub-Source', 'SubSource', 'LeadSource_295', 'Source',
        'SourceCode', 'source_code', 'SourceSubID']
  </code></pre>
  
  <p>I am iterating over XML in python to create a dictionary for each child node. The dictionary varies in length and keys with each iteration. Sometimes the dictionary will contain a key that is also an item in this list. Sometimes it wont. What I want to be able to do is, if a key in the dictionary is also an item in this list then append the value to a new list. If none of the keys in the dictionary are in list source, I'd like to append a default value. I'm really having a brain block on how to do this. Any help would be appreciated. </p>