python 高阶函数:filter(过滤器)

官网解释：

• filter(function, iterable)

• Construct a list from those elements of iterable for which function returns true. iterable may be either a sequence, a container which supports iteration, or an iterator. If iterable is a string or a tuple, the result also has that type; otherwise it is always a list. If function is None, the identity function is assumed, that is, all elements of iterable that are false are removed.

  Note that filter(function, iterable) is equivalent to [item for item in iterable if function(item)] if function is not None and [item for itemin iterable if item] if function is None.

  See itertools.ifilter() and itertools.ifilterfalse() for iterator versions of this function, including a variation that filters for elements where the function returns false.

• str.strip([chars])

• Return a copy of the string with the leading and trailing characters removed. The chars argument is a string specifying the set of characters to be removed. If omitted or None, the chars argument defaults to removing whitespace. The chars argument is not a prefix or suffix; rather, all combinations of its values are stripped:

  >>> '   spacious   '.strip()
  'spacious'
  >>> 'www.example.com'.strip('cmowz.')
  'example'

就是，如果省略参数，默认过滤空格。

#过滤list中的偶数

def get_odd(s):
    return s % 2 == 1;   #C语言绝对不能这么写
   
print "get odd:", filter(get_odd, [1, 2, 3, 4, 5, 6])

#过滤list中的空格

def not_empty(s):
    return s and s.strip()   #s过滤了'None'元素，s.strip()默认过滤空格
   
print "not_empty:", filter(not_empty, ['A', ' ', 'B', None, 'C', '  '])

补充：

.strip(None/string)：从头尾开始，按对象字符串顺序删除

a.如果strip参数中没有对象头尾开始的字符，则无法删除，返回对象全字符

str1 = 'www.example.com'
print (str1.strip('lcoz.'))

  ####strip参数中没有'w'/'m'，两端删除受阻

b.如果strip参数中有对象的头尾开始字符，则匹配删除参数中的字符，返回未删除字符

str1 = 'www.example.com'
print (str1.strip('lcwmeoza.'))

xamp   ####strip参数中没有'x'/'p',两端删除受阻