filter()和map一样，接收一个函数和一个序列。和map不同的是，filter()把传入的函数依次作用于每个元素，然后根据返回值是True还是False决定保留还是丢弃该元素

过滤出奇数：

def   is_odd(n):    return n%2==1print  filter(is_odd,[1,2,3,4,5])    # ==>[1, 3, 5]

 过滤掉空字符串：

def   not_empty(s):    return  s  and  s.strip()     print  filter(not_empty,['A','','B',None,'C','  '])   # ==>['A', 'B', 'C']

 

L=range(1,101)def  iseven(x):    return  x%2==0print filter(iseven,L)#[2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100]