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<H1><A NAME="SECTION000700000000000000000">
6 PEP 322: Reverse Iteration</A>
</H1>

<P>
A new built-in function, <tt class="function">reversed(<var>seq</var>)</tt>, takes a sequence
and returns an iterator that loops over the elements of the sequence
in reverse order.

<P>
<div class="verbatim"><pre>
&gt;&gt;&gt; for i in reversed(xrange(1,4)):
...    print i
...
3
2
1
</pre></div>

<P>
Compared to extended slicing, such as <code>range(1,4)[::-1]</code>,
<tt class="function">reversed()</tt> is easier to read, runs faster, and uses
substantially less memory.

<P>
Note that <tt class="function">reversed()</tt> only accepts sequences, not arbitrary
iterators.  If you want to reverse an iterator, first convert it to
a list with <tt class="function">list()</tt>.

<P>
<div class="verbatim"><pre>
&gt;&gt;&gt; input = open('/etc/passwd', 'r')
&gt;&gt;&gt; for line in reversed(list(input)):
...   print line
...
root:*:0:0:System Administrator:/var/root:/bin/tcsh
  ...
</pre></div>

<P>
<div class="seealso">
  <p class="heading">See Also:</p>

<dl compact="compact" class="seerfc">
    <dt><a href="http://www.python.org/peps/pep-0322.html"
        title="Reverse Iteration"
        >PEP 322, <em>Reverse Iteration</em></a>
    <dd>Written and implemented by Raymond Hettinger.
  </dl>

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