string 模块 maketrans函数 和 translate函数的用法

1.

string.maketrans(from, to)
Return a translation table suitable for passing to translate(), that will map each character in from into the character at the same position in to; from and to must have the same length.

2.

string.translate(s, table[, deletechars])
Delete all characters from s that are in deletechars (if present), and then translate the characters using table, which must be a 256-character string giving the translation for each character value, indexed by its ordinal. If table is None, then only the character deletion step is performed.

例子1：

from string import maketrans   # Required to call maketrans function.

intab = "aeiou"
outtab = "12345"
trantab = maketrans(intab, outtab)

str = "this is string example....wow!!!";
print str.translate(trantab);

输出结果：

>>> 

th3s 3s str3ng 2x1mpl2....w4w!!!

例子2：

from string import maketrans   # Required to call maketrans function.

intab = "aeiou"
outtab = "12345"
trantab = maketrans(intab, outtab)

str = "this is string example....wow!!!";
print str.translate(trantab, 'xm');

输出结果:

th3s 3s str3ng 21pl2....w4w!!!

例子3：

引用自：Python Cookbook 第二版， 1.9节

使用字符串的方法translate，为了使用更方便，对它进行一个封装。

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:

        #定义一个翻译表allchars，且指定不须翻译。

        allchars = string.maketrans('', '')

        delete = allchars.translate(allchars, keep.translate(allchars, delete))

    def translate(s):

        return s.translate(trans, delete)

    return translate

NameAndID = 'FuQiang 61450597'

degits_only = translator(keep=string.digits)

print type(degits_only)

ID = degits_only(NameAndID)

print ID

no_digits = translator(delete=string.digits)

name = no_digits(NameAndID)

print name

digits_to_hash = translator(frm=string.digits, to='*')

hideID = digits_to_hash(NameAndID)

print hideID

delete_keep = translator(delete='Fu', keep = 'qiang6145')

partStr = delete_keep(NameAndID)

print partStr

输出结果 ：

>>> 

<type 'function'>

61450597

FuQiang 

FuQiang ********

iang61455

>>> 

例子4：

引用自：Python Cookbook 第二版， 1.10节

过滤字符串中不属于指定集合的字符

import string

#maketrans函数是一个创建翻译表的工具函数。

allchars = string.maketrans('', '')

def makefilter(keep):

    delchars = allchars.translate(allchars, keep)

    def thefilter(s):

        return s.translate(allchars, delchars)

    return thefilter

if __name__ == '__main__':

    filterStr = makefilter('abcdefg')

    print filterStr('FuQiang')

输出：

>>> 

ag

>>>