map和filter

def fun (x):
    return x**2
a = [1,2,3,4,5]
b = list(map(f,a))
//or
b = [x for x in map(f,a)]//1，4，9，16，25

def fun(n):
    return n%2 == 0
a = [1,2,3,4]
b = [x for x in filter(fun,a)] //b =[2,4]