学习python3 06 map/reduce

map

def f(x):...     return x * x//结果r是一个Iteratorr = map(f, [1, 2, 3, 4, 5, 6, 7, 8, 9])list(r)[1, 4, 9, 16, 25, 36, 49, 64, 81] list(map(str, [1, 2, 3, 4, 5, 6, 7, 8, 9]))['1', '2', '3', '4', '5', '6', '7', '8', '9']

reduce

reduce把一个函数作用在一个序列[x1, x2, x3, …]上，这个函数必须接收两个参数，reduce把结果继续和序列的下一个元素做累积计算，其效果就是：

reduce(f, [x1, x2, x3, x4]) = f(f(f(x1, x2), x3), x4)from functools import reducedef fn(x, y):...     return x * 10 + y...reduce(fn, [1, 3, 5, 7, 9])13579from functools import reduce def fn(x, y):...     return x * 10 + y... def char2num(s):...     return {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4, '5': 5, '6': 6, '7': 7, '8': 8, '9': 9}[s]... reduce(fn, map(char2num, '13579'))13579