The function reduce has been “banned” to the functools module!
reduce(function, sequence[, initial]) -> value
Apply a function of two arguments cumulatively to the items of a sequence, from left to right, so as to reduce the sequence to a single value.
If initial is present, it is placed before the items of the sequence in the calculation, and serves as a default when the sequence is empty.
[s1, s2, s3, s4]
func(s1,s2)
func(func(s1,s2),s3)
func(func(func(s1,s2),s3),s4)