rreplace-如何替换字符串中表达式的最后一次出现？
问题内容：
Python中是否有一种快速的方法来替换字符串，而不是像从头开始那样replace从头开始呢？例如：
>>> def rreplace(old, new, occurrence)
>>> ... # Code to replace the last occurrences of old by new
>>> '<div><div>Hello</div></div>'.rreplace('</div>','</bad>',1)
>>> '<div><div>Hello</div></bad>'
问题答案：
>>> def rreplace(s, old, new, occurrence):
... li = s.rsplit(old, occurrence)
... return new.join(li)
...
>>> s
'1232425'
>>> rreplace(s, '2', ' ', 2)
'123 4 5'
>>> rreplace(s, '2', ' ', 3)
'1 3 4 5'
>>> rreplace(s, '2', ' ', 4)
'1 3 4 5'
>>> rreplace(s, '2', ' ', 0)
'1232425'
