Python的string.maketrans 过滤字符串的问题

源自Python cookbook 记录下来，以免今后忘记了。

简化字符串的translate的方法

#translate_v1.py
#!/usr/bin/python

import string
def translator(frm='', to='', delete='', keep=None):
    if len(to) == 1:
        to = to * len(frm)
    trans = string.maketrans(frm, to)
    if keep is not None:
        allchars = string.maketrans('', '')
        delete = allchars.translate(allchars, keep.translate(allchars, delete))

    def translate(s):
        return s.translate(trans, delete)
    return translate

执行如下：

In [1]: import translate_v1
In [2]: import string
In [3]: digits_only = translate_v1.translator(keep=string.digits)
In [4]: digits_only('Chris Perkins : 224-7992')
Out[4]: '2247992'
In [5]: no_digits = translate_v1.translator(delete=string.digits)
In [6]: no_digits('Chris Perkins : 224-7992')
Out[6]: 'Chris Perkins : -'
In [7]: digits_to_hash = translate_v1.translator(frm='string.digits', to='#')
In [8]: digits_to_hash('Chris Perkins: 224-7992')
Out[8]: 'Chris Perkins: ###-####'

过滤字符串中不属于指定集合的字符

#!/usr/bin/python

import string

allchars = string.maketrans('', '')
def makefilter(keep):
    delchars = allchars.translate(allchars, keep)
    def thefilter(s):
        return s.translate(allchars, delchars)
    return thefilter


if __name__ == "__main__":
    just_vowels = makefilter('aeiouy')
    print just_vowels('four sore and seven years ago')