Python Regex 匹配除以主题标签开头的单词之外的所有内容

Question

I'm trying to match all the words that do not start with a hashtag using Python Regex.

Example sentence:

    This is #a test for #matching #hashtags

I would like the following to be matched: This is test for

I was able to match all the words that start with a hashtag with this: #\\b\\w *

Then I realized I needed the opposite.

I tried many variation similar to these without success:

• ^(?#\\b\\w*)
• ^(?!#)\\w+$
• ^(?!#).*
• /([\\s\\S]*?)(#)
• ^(?:(?!#).)*$

Nothing works.

Answer 1

If you want a Regex, you will need a Negative Lookbehind

(?<!#)\\b\\w+

https://regex101.com/r/aMdc7R/1

Answer 2

A non-regex solution should be fine:

>>> text = 'This is #a test for #matching #hashtags'
>>> [word for word in text.split(' ') if not word.startswith('#')]
['This', 'is', 'test', 'for']

For regex, you need to use something like negative lookbehind assertion, which will match only if the substring is not preceded by substring/character specified.

Answer 3

To prevent firing the lookbehind on every position before a match, you can switch the word boundary and the lookbehind (as lookarounds can be expensive) and the lookbehind fires after asserting the word boundary.

\b(?<!#)\w+

• \\b A word boundary
• (?<!#) Negative lookbehind, assert not # directly to the left of the current position
• \\w+ Match 1+ word characters

Regex demo