reduce

In Python 2 it was still part of the language.

reduce(function, iterable[, initializer])

from functools import reduce

numbers = [1, 2, 3, 4]

print(reduce(lambda x,y: x+y, numbers))    # 10  = ((1+2)+3)+4
print(reduce(lambda x,y: x*y, numbers))    # 24  = ((1*2)*3)*4
print(reduce(lambda x,y: x/y, [8, 4, 2]))  # 1.0 = (8/4)/2

print(reduce(lambda x,y: x+y, [2]))        # 2
print(reduce(lambda x,y: x*y, [2]))        # 2

Output:

10
24
1.0
2
2

The initializer is used as the 0th element returned by the iterable. It is mostly interesting in case the iterable is empty.