Reset list 'a'

The result of the previous block containing the map example left 'a' to be [6, 7, 8], so resetting 'a'  back to [3, 4, 5] seems to keep the example in line with the other ones.

docs/writing/style.rst

@@ -543,6 +543,7 @@ Use :py:func:`enumerate` keep a count of your place in the list.
 
 .. code-block:: python
 
+    a = [3, 4, 5]
     for i, item in enumerate(a):
         print i, item
     # prints