仅替换字符串的结尾

看起来你应该能够做到这一点而不分裂成一个数组。找到最后一个 . 然后切到那里:

> given_string = "first.second.third.None"
> given_string[:given_string.rfind('.')] + '.fourth'

'first.second.third.fourth'

你可以试试这个:

given_string = "first.second.third.None"
given_string = ".".join(given_string.split('.')[:-1] + ["fourth"])
print(given_string)

产量:

first.second.third.fourth

试试这一行:

print (".".join(given_string.split(".")[:-1]+["Fourth"]))

产量:

first.second.third.Fourth

你可以用rsplit。不管最后一次拆分之前有多少个点,这都会起作用

given_string = "first.second.third.None"
string_splitted = given_string.rsplit('.', 1)[0] + '.fourth'

print(string_splitted)
first.second.third.fourth

my_string = "first.second.third.None"
my_sub = re.sub(r'((\w+\.){3})(\w+)', r'\1fourth', my_string)
print(my_sub)
first.second.third.fourth

下面是对这种风格的一个很好的解释: How to find and replace nth occurence of word in a sentence using python regular expression?