Python reduce() 函數

Python reduce() 函數

在調用該函數之前，先要導入該函數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

通俗解釋：reduce(function, sequence): function是一個函數，sequence是一個數據集合（元組、列表等）。先將集合里的第1，2個參數參入函數執行，再將執行結果和第3個參數傳入函數執行....,最終得到最后一個結果

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

先將1，2傳入：1+2 = 3

再將3，3傳入：3+3 = 6

再將6，4傳入：6+4 = 10

最終結果為：10

習題

Python 一個數如果恰好等於它的因子之和，這個數就稱為"完數"。例如6=1+2+3.編程找出 1000 以內的所有完數

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)