title: Intersecting two dictionaries
body: <p>I am working on a search program over an inverted index. The index itself is a dictionary whose keys are terms and whose values are themselves dictionaries of short documents, with ID numbers as keys and their text content as values. </p>
  
  <p>To perform an 'AND' search for two terms, I thus need to intersect their postings lists (dictionaries). What is a clear (not necessarily overly clever) way to do this in Python? I started out by trying it the long way with <code>iter</code>:</p>
  
  <pre><code>p1 = index[term1]  
  p2 = index[term2]
  i1 = iter(p1)
  i2 = iter(p2)
  while ...  # not sure of the 'iter != end 'syntax in this case
  ...
  </code></pre>