python - 正则表达式:仅替换一次

Question

我正在尝试使用正则表达式仅替换字符串中特定单词的一个实例，其中需要替换的单词至少出现两次。例如我有以下内容:

The NOUN is ADJECTIVE and is completely different from the NOUN.

到目前为止我有:

content = 'The NOUN is ADJECTIVE and is completely different from the NOUN.'   

noun = input('Enter a noun: ')
adj = input('Enter an adjective: ')
noun_1 = input('Enter another noun: ')

names_regex_noun = re.compile(r'NOUN')
content = names_regex_noun.sub(noun, content)
names_regex_adj = re.compile(r'ADJECTIVE')
content = names_regex_adj.sub(adj, content)
names_regex_noun_1 = re.compile(r'NOUN')
content = names_regex_noun_1.sub(noun_1, content) 
print(content)

我遇到的问题是在使用 names_regex_noun.sub(noun, content) 时它正在替换 NOUN 的两个实例在 content .我只想替换第一个并保留 NOUN 的第二个实例不受影响，因此可以用 noun_1 代替.

Answer 1

对于像这样的简单表达式，你可以只使用str.replace()具有指定的 count:

>>> content = 'The NOUN is ADJECTIVE and is completely different from the NOUN.'
>>> noun = 'bird'
>>> content.replace('NOUN', noun, 1)
'The bird is ADJECTIVE and is completely different from the NOUN.'