python 3.0以后, reduce已经不在built-in function里了, 要用它就得from functools import reduce.
reduce的用法
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.
意思就是对sequence连续使用function, 如果不给出initial, 则第一次调用传递sequence的两个元素, 以后把前一次调用的结果和sequence的下一个元素传递给function. 如果给出initial, 则第一次传递initial和sequence的第一个元素给function.
? 1 2 3 4 5 6 7 from functools import reduce reduce ( lambda x,y: x + y, [ 1 , 2 , 3 ]) 输出 6 reduce ( lambda x, y: x + y, [ 1 , 2 , 3 ], 9 ) 输出 15 reduce ( lambda x,y: x + y, [ 1 , 2 , 3 ], 7 ) 输出 13
＊functool标准库还有很多功能，可以参考网上的资料
转自：http://www.cnblogs.com/alan-babyblog/p/5194399.html
