0004python中的map，reduce，lambda，filter

编程实现：a[0]*b[0] + a[1]*b[1] +...+a[i]*b[j]

>>> a=[1,2,3,4,5]
>>> b=[6,7,8,9,0]

>>> from functools import reduce
>>> from operator import add,mul
>>> reduce(add,map(mul,a,b))
80

>>> filter(lambda x:x>2,a)
[3, 4, 5]