Reduce

reduce（）函数接收两个参数：函数和可迭代对象，计算过程如下：

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

 

求和1到100:

>>> from functools import reduce
>>> def add(x,y):
    return x+y

>>> reduce(add,list(range(101)))
5050

用自带sum( )函数实现：

>>> sum(list(range(101)),) a、sum()接收两个参数：可迭代对象和初始值，初始值不写默认为0. b、range(101)得到从0到100
5050

 

将整数序列［1，3，5，7，9］变成整数13579:

>>> from functools import reduce
>>> def fn(x,y):
    return x*10+y

>>> reduce(fn,[1,3,5,7,9])
13579

 

str2int：（用map把str变成序列再用reduce变序列为整数）

>>> from 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]             （字典通过key取value s为对应的key）

>>> reduce(fn,map(char2num,'13579')) 将map得到的iterator直接作为reduce的iterable
13579

 

 

reduce接收list求所有元素积

>>> from functools import reduce
>>> def prod(x,y):
    return x*y

>>> reduce(prod,[3,5,7,9])
945

 

转载于:https://www.cnblogs.com/sniperlr/p/7286578.html