filter用法：
#!/usr/bin/env python3
... #-*-coding:utf-8-*-
...
>>> def is_odd(n):
... return n % 2 == 1
...
>>> L = range(100)
>>>
>>> print(list(filter(is_odd,L)))
[1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99]
>>>
>>>
>>> def not_empty(s):
... return s and s.strip()
...
>>> print(list(filter(not_empty,['A','','B',None,'C',' '])))
['A', 'B', 'C']
