替换文本中最后一次出现的字符串

Question

假设我有这段文字：

Saturday and Sunday and Monday and Tuesday and Wednesday and Thursday and Friday are days of the week.  

我希望除了最后一个and以外的所有内容都替换为逗号：

Saturday, Sunday, Monday, Tuesday, Wednesday, Thursday and Friday are days of the week. 

在正则表达式中有一种简单的方法吗？据我所知，正则表达式中的replace方法一直在替换字符串。

Answer 1

str.replace()方法有一个count参数：

  

str.replace(old, new[, count])

     

返回字符串的副本，其中所有出现的substring old都替换为new。如果给出了可选参数计数，则仅替换第一次计数出现次数。

然后，使用str.count()检查字符串中and的数量，然后-1（因为您需要最后一个and）：

  

str.count(sub[, start[, end]])

     

返回[start, end]范围内子串sub的非重叠出现次数。可选参数start和end被解释为切片表示法。

演示：

>>> string = 'Saturday and Sunday and Monday and Tuesday and Wednesday and Thursday and Friday are days of the week.'   
>>> string.replace(' and ', ", ", (string.count(' and ')-1))
'Saturday, Sunday, Monday, Tuesday, Wednesday, Thursday and Friday are days of the week.  '

Answer 2

如果你想要一个正则表达式解决方案，你可以匹配所有and s后面的字符串中的另一个>>> str='Monday and Tuesday and Wednesday and Thursday and Friday and Saturday and Sunday are the days of the week.' >>> import re >>> re.sub(' and (?=.* and )', ', ', str) 'Monday, Tuesday, Wednesday, Thursday, Friday, Saturday and Sunday are the days of the week.' 。

(?=

) ... 8.8.8.8是一个先行，它确保在字符串中稍后匹配，而不在实际匹配中包含它（因此也不在替换中）。这有点像比赛的条件。