rreplace - 如何替换字符串中最后一次出现的表达式？

Question

Python中是否有一种快速的方法来替换字符串,但是从头开始,而不是从头开始replace？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>'

Answer 1

>>> 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'

Answer 2

这是一个单行：

result = new.join(s.rsplit(old, maxreplace))

返回字符串s的副本，其中所有出现的子字符串old 都被new替换。第一个maxreplace出现被替换。

以及使用中的完整示例：

s = 'mississipi'
old = 'iss'
new = 'XXX'
maxreplace = 1

result = new.join(s.rsplit(old, maxreplace))
>>> result
'missXXXipi'

Answer 3

只需反转字符串，替换第一次出现并再次反转它：

mystr = "Remove last occurrence of a BAD word. This is a last BAD word."

removal = "BAD"
reverse_removal = removal[::-1]

replacement = "GOOD"
reverse_replacement = replacement[::-1]

newstr = mystr[::-1].replace(reverse_removal, reverse_replacement, 1)[::-1]
print ("mystr:", mystr)
print ("newstr:", newstr)

输出：

mystr: Remove last occurence of a BAD word. This is a last BAD word.
newstr: Remove last occurence of a BAD word. This is a last GOOD word.

Answer 4

我不会假装这是最有效的方法,但这是一种简单的方法.它会反转所有相关字符串,使用str.replace反向字符串执行普通替换,然后以正确的方式反转结果:

>>> def rreplace(s, old, new, count):
...     return (s[::-1].replace(old[::-1], new[::-1], count))[::-1]
...
>>> rreplace('<div><div>Hello</div></div>', '</div>', '</bad>', 1)
'<div><div>Hello</div></bad>'

Answer 5

如果您知道“旧”字符串不包含任何特殊字符，您可以使用正则表达式：

In [44]: s = '<div><div>Hello</div></div>'

In [45]: import re

In [46]: re.sub(r'(.*)</div>', r'\1</bad>', s)
Out[46]: '<div><div>Hello</div></bad>'