title: Python filter() function
body: <pre><code>filter(function,  an_iter)
  *If the iterable an_iter is a sequence, then the returned value is of that same type, 
  otherwise the returned value is a list.* 
  </code></pre>
  
  <p>I came across the above description as part of the definition for the <code>filter(func, a_sequence)</code>  function in Python. </p>
  
  <p>I understand how <code>filter</code> works on a sequence type (lists, strings, tuples).  However, can you give me situations where a  non-sequence type is the <code>an_iter</code> parameter and what kind of result would form?</p>