Question

I’m trying to use python re to find a set of the same letter or number repeated a specific number of times. (.) works just fine for identifying what will be repeated, but I cannot find how to keep it from just repeating different characters. here is what I have:

re.search(r'(.){n}', str)

so for example it would match 9999 from 99997 if n = 4, but not if n = 3.
thanks

Answer 1

How about

(?:^|(?<=(.)))(?!\1)(.)\2{n-1}(?!\2)

This will:

• (?:^|(?<=(.))): Make sure that:
  • ^: Either we are at the beginning of the string
  • (?<=(.)): Either we are not at the beginning of the string; then, capture the character before the match and save it into \1
• (?!\1)(.): Match any character that is not \1 and save it into \2
• \2{n-1}: Match \2 n-1 times
• (?!\2): Make sure \2 cannot be matched looking forward

(The n-1 is only symbolic; obviously you want to replace this with the actual value of n-1, not with 8-1 or something).

Important edit: The previous version of the regex ((.)\1{n-1}(?!\1)) does not work because it fails to account for character matching \1 behind the match. The regex above fixes this problem.