title: Only index needed: enumerate or (x)range?
body: <p>If I want to use only the index within a loop, should I better use the <code>range/xrange</code> function in combination with <code>len()</code> </p>
  
  <pre><code>a = [1,2,3]
  for i in xrange(len(a)):
      print i 
  </code></pre>
  
  <p>or <code>enumerate</code>? Even if I won't use <code>p</code> at all? </p>
  
  <pre><code>for i,p in enumerate(a):
      print i    
  </code></pre>