title: What happened to ifilter?
body: <p>In comparing documentation for itertools between Python <a href="https://docs.python.org/2/library/itertools.html" rel="noreferrer">2</a> and <a href="https://docs.python.org/3/library/itertools.html" rel="noreferrer">3</a>, I noticed <code>ifilter</code>, <code>imap</code>, <code>izip</code> are missing from Python 3.  I suspect this is because many builtin keywords have been converted to generators and replaced former keywords, but it is unclear in this case.  </p>
  
  <p>Is it true <code>ifilter</code>, <code>imap</code>, <code>izip</code> are now equivalent to <code>filter</code>, <code>map</code>, <code>zip</code> in Python 3?  If not, where can I find rationales for why certain methods were removed from current <code>itertools</code>?</p>