CODEWITHSUNDEEP
pythonregexregex-lookaroundsregex-groupregex-negation
dgor
dgor

Reputation: 862

Quantifiers inside a positive look-behind using Python

I am trying to capture a group only if the lookbehind positive criteria satisfies.

Input string is either of the below

  1. Cats 5A, 5B and 5C
  2. Cat 5A

Regex:

  1. (?P<cat_num>(?:(?<=((\b[c|C]at)[s]? )))5A) ==> Incorrect because of quantifier present in lookbehind.
  2. (?P<cat_num>(?:(?<=((\b[c|C]at)(?=[s]?) )))5A) ==> Correct but does not match "5A" when Input 1 is given.

Requirement:

Using Python regex, I want to capture "5A" in capturing group cat_num when any of the above two inputs are given.

Upvotes: 1

Views: 163

Answers (1)

The fourth bird
The fourth bird

Reputation: 163517

You don't need a lookbehind assertion. You could match what comes before the number, and capture the value in the named capturing group cat_num

Make the s optional using [cC]ats?

\b[cC]ats? (?P<cat_num>5A)\b

Regex demo

Or a bit broader match:

\b[cC]ats? (?P<cat_num>\d+[A-Z]+)\b

Regex demo

Upvotes: 1

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