Recipe 1.10. Filtering a String for a Set of Characters(Python Cookbook)

 1 >>> import string
 2 >>> allchars = string.maketrans('', '')
 3 >>> def makefilter(keep):
 4     delchars = allchars.translate(allchars, keep)
 5     def thefilter(s):
 6         return s.translate(allchars, delchars)
 7     return thefilter
 8 
 9 >>> just_vowels = makefilter('aeiouy')
10 >>> print just_vowels('four score and seven years ago')
11 ouoeaeeyeaao
12 >>> print just_vowels('Hello Ray Zhang')
13 eoaya
14 
15 >>> import sets
16 >>> class Keeper():
17     def __init__(self, keep):
18         self.keep = sets.Set(map(ord, keep))
19     def __getitem__(self, n):
20         if n not in self.keep:
21             return None
22         return unichr(n)
23     def __call__(self, s):
24         return unicode(s).translate(self)
25 
26 >>> makefilter = Keeper
27 >>> just_vowels = makefilter('aeiouy')
28 >>> print just_vowels(u'four score and seven years ago')
29 ouoeaeeyeaao
30 >>> print just_vowels(u'Hello Ray Zhang')
31 eoaya
32