内置函数起始值

ref:

http://mp.weixin.qq.com/s?__biz=MjM5NzU0MzU0Nw==&mid=211637608&idx=1&sn=1aa3d81c2c56fc87533c49f912692742&scene=0&key=dffc561732c22651a58840064393fadfff612048d19d8fde33d3062e3072d56b15a4c6f3346a0b8fcd142ef0607dbf92&ascene=1&uin=MjI2MTM3MDUwMA%3D%3D&devicetype=webwx&version=70000001&pass_ticket=Z7bdKMF60ppUTY3aii%2BXlJ2hbVAiWlXhZJOa22Y5qV8ugvvf%2BiChYRBPEyxp3KSq

第一个就蒙了，reduce怎么出来这么多参数，尤其最后一个不理解

后来试了下：

>>> reduce(lambda x,y:x+y,range(101),1)
5051

1应该是个起始值，但后面紧跟着的操作，是把range产生的 0赋值给y继续，还是赋值给x继续,不清楚

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.

到目前为止还见过有起始值的enumerate

t=range(10)
>>> for index,value in enumerate(t,start=1):
    print index,value

1 0
2 1
3 2
4 3
5 4
6 5
7 6
8 7
9 8
10 9

以及sum

>>> sum(range(0,101),1)
5051