使用 re.sub() 时无效的组引用 [英] invalid group reference when using re.sub()

问题描述

我在使用 re.sub 时遇到了麻烦.我从其他答案中了解到这是因为我引用了一个我没有的捕获组.

I'm having troubles with re.sub. I understand from other answers that this is due to the fact I'm referencing to a capturing group that I don't have.

我的问题是:如何调整我的代码以拥有一个有效的组?

My question is: how do I adjust my code to have a valid group?

s = "hello a world today b is sunny c day"
markers = "a b c".split()
pattern = r'\b' + ' (?:\w+ )?(?:\w+ )?'.join(markers) + r'\b'
text = re.sub(pattern, r'<b>\1</b>', s)   # this gives error

我想要这个:hello a world today b is nice c day"

I want to have this : "hello <b>a world today b is sunny c</b> day"

推荐答案

如果模式中没有捕获组，则不能使用 \1 替换反向引用.将捕获组添加到模式:

You cannot use \1 replacement backreference if there are no capturing groups in the pattern. Add the capturing group to the pattern:

pattern = r'\b(' + ' (?:\w+ )?(?:\w+ )?'.join(markers) + r')\b' # or
              ^                                            ^
pattern = r'\b({})\b'.format(r' (?:\w+ )?(?:\w+ )?'.join(markers))

或者，只需使用 \g<0> 插入整个匹配项而不是捕获组值(然后，无需修改您的正则表达式):

Or, just use the \g<0> to insert the whole match rather than a capturing group value (then, there is no need amending your regex):

text = re.sub(pattern, r'<b>\g<0></b>', s) 

请参阅 Python 演示.

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