Python Regex Variable Negative Lookbehind

Question

I am trying to find the occurrence of various terms that are not preceded by another group of terms. Normally if I would have a single term in the preceding group I could use a negative lookbehind, but at Python has a zero-width assumption this doesn't seem to be the case. The only solution I see is to run two regexes, one for the presence of what I am looking for and another to confirm the non-existence of the preceding group terms. There must be a more elegant and efficient way of doing this. Can anyone help?

The test sentence is:

10 day trip excludes flights

The regex that assures that it isn't matched due to the word 'flights' being preceded by 'excludes' is the following:

(?:without|not including|doesn\'?t include|exclud(?:es|ing))\s*(?:flights?(?:\s+tickets)?|airfare|airline tickets?)

However I want to assure that certain text is included. I can confirm this with the following:

(?:flights?(?:\s+tickets)?|airfare|airline tickets?)

So this would match 'including ticket' and 'and airfare' but not 'without flight tickets'

Some examples of matching strings are:

including flights
includes flights
plus flights
flights are included
including airfare
and airfare

Some examples of non-matching strings are:

not including flights
flights are not included
excluding flights
without airfare

That's the base. However that matches anything not preceded by those particular terms. You can see an example here: regex101.com/r/kA0mL3/4 — user2694306
– user2694306, Commented Aug 21, 2014 at 18:19

Avinash Raj · Accepted Answer · 2014-08-21 18:40:26Z

2

You could try the below regex,

^(?=.*?(?:flights|airfare))(?:(?!without|not includ(?:ing|ed)|doesn\'?t include|exclud(?:es|ing)).)*$

DEMO

answered Aug 21, 2014 at 18:40

Avinash Raj

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1 Comment

user2694306 Over a year ago

That's awesome, I didn't think of using a look forward.

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