Python 函数 —— map(), reduce()

map()函数接收两个参数，一个是函数，一个是Iterable，map将传入的函数依次作用到序列的每个元素，并把结果作为新的Iterator返回。

In [9]: a=[1]*10 In [10]: a Out[10]: [1, 1, 1, 1, 1, 1, 1, 1, 1, 1] In [11]: def my_double(x): ...: return 2*x ...: In [12]: map(my_double, a) Out[12]: <map at 0x281d5a99d30> In [13]: list(map(my_double, a)) Out[13]: [2, 2, 2, 2, 2, 2, 2, 2, 2, 2]

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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) In [16]: from functools import reduce In [10]: a Out[10]: [1, 1, 1, 1, 1, 1, 1, 1, 1, 1] In [14]: def my_sum(x,y): ...: return x+y ...: In [18]: reduce(my_sum, a) Out[18]: 10

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In [19]: a='wqeqeqweqweqeqweqwe' In [20]: b='wqeqeqweqwreqeqweqwe' In [21]: c=list(map(ord,a+b)) In [22]: c Out[22]: [119, 113, 101, 113, 101, 113, 119, 101, 113, 119, 101, 113, 101, 113, 119, 101, 113, 119, 101, 119, 113, 101, 113, 101, 113, 119, 101, 113, 119, 114, 101, 113, 101, 113, 119, 101, 113, 119, 101] In [23]: import operator In [24]: reduce(operator.xor, c) Out[24]: 114 In [25]: chr(114) Out[25]: 'r'