Python reduce() 函数

Python reduce() 函数

在调用该函数之前，先要导入该函数from functools import reduce

def reduce(function, sequence, initial=None): # real signature unknown; restored from __doc__
    """
    reduce(function, sequence[, initial]) -> value
    
    Apply a function of two arguments cumulatively to the items of a sequence,
    from left to right, so as to reduce the sequence to a single value.
    For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates
    ((((1+2)+3)+4)+5).  If initial is present, it is placed before the items
    of the sequence in the calculation, and serves as a default when the
    sequence is empty.
    """
    pass

通俗解释：reduce(function, sequence): function是一个函数，sequence是一个数据集合（元组、列表等）。先将集合里的第1，2个参数参入函数执行，再将执行结果和第3个参数传入函数执行....,最终得到最后一个结果

比如：reduce(lambda x, y: x + y,[1,2,3,4])执行步骤：

先将1，2传入：1+2 = 3

再将3，3传入：3+3 = 6

再将6，4传入：6+4 = 10

最终结果为：10

习题

Python 一个数如果恰好等于它的因子之和，这个数就称为"完数"。例如6=1+2+3.编程找出 1000 以内的所有完数

from functools import reduce
for i in range(2, 1001):
    l = [1]
    for j in range(2, int(i / 2 + 1)):
        if i % j == 0:
            l.append(j)
    if i == reduce(lambda x,y: x+y, l):
        print(i)