一、map()函数
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。
1 >>> from collections import Iterator 2 >>> def f(x): 3 ... return x * x 4 ... 5 >>> r = map(f, [1, 2, 3, 4, 5]) 6 >>> r 7 <map object at 0x1013e5748> 8 >>> isinstance(r, Iterator) 9 True 10 >>> list(r) 11 [1, 4, 9, 16, 25]
二、reduce()函数
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)
1 >>> from functools import reduce 2 >>> def ad(x, y): 3 ... return x + y 4 ... 5 >>> reduce(ad, [1, 3, 5, 7, 9]) 6 25
1 >>> from functools import reduce 2 >>> DIGITS = {‘0‘: 0, ‘1‘: 1, ‘2‘: 2, ‘3‘: 3, ‘4‘: 4, ‘5‘: 5, ‘6‘: 6, ‘7‘: 7, ‘8‘: 8, ‘9‘: 9} 3 >>> def char2num(s): 4 ... return DIGITS[s] 5 ... 6 >>> def str2int(s): 7 ... return reduce(lambda x, y: x * 10 + y, map(char2num, s)) 8 ... 9 >>> str2int(‘123456‘) 10 123456
时间: 2024-11-01 22:47:33