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Python/sum函数

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# 序列求和
print(sum([1,2,3,4,5,6,7,8,9,]))
# sum函数的原型是sum(iterable,start).可以设置一个初始值
print(sum([1,2,3,4,5,6,7,8,9,],5))
# 展开2层的嵌套列表
iterable = [[1,2],[3,4],[5,6],[7,8]]
print(sum(iterable,[0]))# 后面的start可以为空
# sum函数与下列函数等效
start = [0]
for element in iterable:
    start += element
print(start)
start = [0]
# sum 函数可以看作reduce()的特殊情况
from functools import reduce
from operator import add
print(reduce(add,iterable,start))