Answer by Andrew Clark for Finding the average of a list

sum(l) / float(len(l)) is the right answer, but just for completeness you can compute an average with a single reduce:

>>> reduce(lambda x, y: x + y / float(len(l)), l, 0)20.111111111111114

Note that this can result in a slight rounding error:

>>> sum(l) / float(len(l))20.111111111111111