python替换第n个字符串_替换字符串中第n个出现的子字符串

参考链接： Python中的replace替换子字符串

我已经想出了下面的方法，它还考虑了替换所有出现在左边或右边的“旧”字符串的选项。当然，由于标准str.replace工作得很好，因此没有替换所有引用的选项。def nth_replace(string, old, new, n=1, option='only nth'):

 """

 This function replaces occurrences of string 'old' with string 'new'.

 There are three types of replacement of string 'old':

 1) 'only nth' replaces only nth occurrence (default).

 2) 'all left' replaces nth occurrence and all occurrences to the left.

 3) 'all right' replaces nth occurrence and all occurrences to the right.

 """

 if option == 'only nth':

 left_join = old

 right_join = old

 elif option == 'all left':

 left_join = new

 right_join = old

 elif option == 'all right':

 left_join = old

 right_join = new

 else:

 print("Invalid option. Please choose from: 'only nth' (default), 'all left' or 'all right'")

 return None

 groups = string.split(old)

 nth_split = [left_join.join(groups[:n]), right_join.join(groups[n:])]

 return new.join(nth_split)