regex.md

Regular Expressions

👋 Errors, improvements or other cool stuff? Let me know! 😀

Add thousand separators

RE_NUMBER_FORMAT = re.compile(r"\B(?=(\d{3})+(?!\d))")
RE_NUMBER_FORMAT.sub(",", str(value))

Explanation

Source: regular expressions 101

/\B(?=(\d{3})+(?!\d))/gm

• \B assert position where \b does not match.
• (?=(\d{3})+(?!\d)) Positive Lookahead: Assert that the Regex below matches.
  • (\d{3})+ 1st Capturing Group
    • + matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy).
      ☝️ A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data.
    • \d matches a digit (equivalent to [0-9]).
    • {3} matches the previous token exactly 3 times.
  • (?!\d) Negative Lookahead: Assert that the Regex below does not match.
    • \d matches a digit (equivalent to [0-9]).
• Global pattern flags:
  • g modifier: global. All matches (don't return after first match).
  • m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string).