python 高階函數:filter(過濾器)

官網解釋：

• 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，如果省略參數，默認過濾空格。

#過濾list中的偶數

def get_odd(s):
    return s % 2 == 1;   #C語言絕對不能這么寫
   
print "get odd:", filter(get_odd, [1, 2, 3, 4, 5, 6])

#過濾list中的空格

def not_empty(s):
    return s and s.strip()   #s過濾了'None'元素，s.strip()默認過濾空格
   
print "not_empty:", filter(not_empty, ['A', ' ', 'B', None, 'C', '  '])

補充：

.strip(None/string)：從頭尾開始，按對象字符串順序刪除

a.如果strip參數中沒有對象頭尾開始的字符，則無法刪除，返回對象全字符

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

  ####strip參數中沒有'w'/'m'，兩端刪除受阻

b.如果strip參數中有對象的頭尾開始字符，則匹配刪除參數中的字符，返回未刪除字符

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

xamp   ####strip參數中沒有'x'/'p',兩端刪除受阻