map/reduce

Map

python的内置map功能

map(f, list)
def f(x):
    return x*x
ex: r = map(f, [1, 2, 3, 4, 5, 6, 7, 8, 9])

Reduce

reduce(f, [x1, x2, x3, x4]) = f(f(f(x1, x2), x3), x4)