title: python quickest way to merge dictionaries based on key match
body: <p>I have 2 lists of dictionaries.  List A is 34,000 long, list B is 650,000 long.  I am essentially inserting all the List B dicts into the List A dicts based on a key match.  Currently, I am doing the obvious, but its taking forever (seriously, like a day).  There must be a quicker way!</p>
  
  <pre><code>for a in listA:
      a['things'] = []
      for b in listB:
          if a['ID'] == b['ID']:
              a['things'].append(b)
  </code></pre>