Python正则表达式否定超前断言

Question

I'm a cs newbie and am currently working to get a python regex pattern like this:

it must contain "stop (at most 10 words inbetween) mail" and do not contain "mail stop".

that is to say,

  "please stop the mail, and I want the mail stop" AND "please stop the mail stop" would be rejected. ("mail stop" pattern spotted)


  "please stop the mail" AND "please stop the mail, I want the mail to stop" both would be accepted.(only "stop ~ mail" pattern is seen, and no "mail stop")

what I currently have is:

import re
pattern = re.compile("(?=(stop\s+(\w+\s+){0,10}mail[^\s]*))(?!mail\s+stop)")
print(pattern.search("please stop the mail, I want the mail to stop").group())

but somehow it doesn't work the way I want.

Any help would be appreciated.

Eric

Answer 1

Assuming you need the entire input string to be returned in the event of a match

>>> pattern = re.compile(".*stop\s+(\w+\s+){0,10}mail(?!(\s+stop|(.*mail stop))).*")
>>> print(pattern.search("please stop the mail, I want the mail to stop"))
<_sre.SRE_Match object at 0x15c43c0>
>>> print(pattern.search("please stop the mail stop"))
None
>>> print(pattern.search("please stop the mail, and I want the mail stop"))
None