【python cookbook】简化字符串的translate 方法的使用

#!/usr/bin/python
# -*- coding: utf-8 -*-

#简化字符串的translate 方法的使用

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))
        #keep.translate(allchars,delete)  表示去掉keep和deleted中共有的字符 

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

测试

>>>digits_only = translator(keep=string.digits)
>>>digits_only ('abcd,1234')

>>> '1234'

keep=string.digits    表示只取keep中数字

translate()

S.translate(table [,deletechars]) -> string

Parameters:

Here is the detail of parameters:

• table: You can use the maketrans() helper function in the string module to create a translation table.

• deletechars: list of characters to be removed from the source string.

Return Value:

It returns a translated copy of the string.

简单来说就是对字符串S移除deletechars包含的字符，然后保留下来的字符按照table里面的字符映射关系映射（比如a变成A）。

无deletechars的例子

#!/usr/bin/python

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);


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

有deletechars的例子

#!/usr/bin/python

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');

#This will produce following result:
th3s 3s str3ng 21pl2....w4w!!!

maketrans()

str.maketrans(intab, outtab]);

Parameters:

Here is the detail of parameters:

• intab: string having actual characters.

• outtab: string having corresponding mapping character.

Return Value:

It returns a translate table to be used translate() function.

Example:

#!/usr/bin/python

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);

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

allchars = string.maketrans('','')  表示所有字符  即使用时无需翻译