> help(filter)
Help on built-in function filter in module __builtin__:
 
filter(...)
 filter(function or None, sequence) -> list, tuple, or string
 
 Return those items of sequence for which function(item) is true. If
 function is None, return the items that are true. If sequence is a tuple
 or string, return the same type, else return a list.
 
>

> def odd(n):
...  return n % 2 == 1
...
> filter(odd, range(10))     # 第一个参数为一般函数
[1, 3, 5, 7, 9]
>
> filter(lambda x: x % 2 == 0, range(10)) # 第一个参数为匿名函数
[0, 2, 4, 6, 8]

> L = [1,'',0,'A',None,[1,2],False,3.14,[],{'a':1}, {}]
> filter(None, L)
[1, 'A', [1, 2], 3.14, {'a': 1}]
>

> L = [[], 1, "", None, False, {}, 3.14, " "]
> map(lambda x:x if x != " " else "default", filter(None, L))
[1, 3.14, 'default']

> L = [1,'',0,'A'," ", None,[1,2],False,3.14,[],{'a':1}, {}]
> filter(lambda s: s and (type(s) != str or len(s.strip()) > 0), L)
[1, 'A', [1, 2], 3.14, {'a': 1}]
>