python - Regex to match digits of specific length

Question

I am looking to match a 15 digit number (as part of a larger regex string). Right now, I have

ddddddddddddddd

but I feel like there must be a cleaner way to do this.

question from:https://stackoverflow.com/questions/4824942/regex-to-match-digits-of-specific-length

Answer 1

If your regex language is Perl-compatible: d{15}.

It is difficult to say how handle the edges (so you don't accidentally grab extra digits) without knowing the outer context in which this snippet will be used. The definitive context-independent solution is this:

(?<!d)d{15}(?!d)

You can put this in the middle of any regex and it will match (and only match) a sequence of exactly 15 digits. It is, however, quite awkward, and usually unnecessary. A simpler version that assumes non-alphanumeric boundaries (e.g., whitespace around the digits) is this:

d{15}

But it won't work if the letters immediately precede or followed the sequence.