title: Is the behaviour of Python's list += iterable documented anywhere?
body: <p>It would appear that in Python, <code>list += x</code> works for any iterable <code>x</code>:</p>
  
  <pre><code>In [6]: l = []
  
  In [7]: l += [1]
  
  In [8]: l += (2, 3)
  
  In [9]: l += xrange(5)
  
  In [10]: l
  Out[10]: [1, 2, 3, 0, 1, 2, 3, 4]
  </code></pre>
  
  <p>Is this behaviour documented anywhere?</p>
  
  <p>To contrast this with <code>list + x</code>, the latter only works if <code>x</code> is also a <code>list</code>. This is spelled out in the <a href="http://docs.python.org/2/library/stdtypes.html#sequence-types-str-unicode-list-tuple-bytearray-buffer-xrange" rel="nofollow noreferrer">documentation</a>.</p>