Sums start and the items of a sequence, from left to right, and
returns the total. start defaults to
0. The items are
normally numbers, and are not allowed to be strings. The fast, correct
way to concatenate sequence of strings is by calling
''.join(sequence). Note that
sum(range(n), m) is equivalent to
reduce(operator.add, range(n), m). New in version 2.3.