213 – Expanding regex matches

Regex matches can be used to expand strings that reference matching groups, allowing you to quickly and conveniently format strings with data extracted from a regex.

You start by getting a regex match using any of the functions that the module re provides:

import re

m = re.search(r"(\d+)\.(\d{2})", "Total: 12.45€")

The regex above extracts the number 12.45 and uses two groups to target the integer and decimal parts of the number.

Then, the method expand of the match can be used to format any string that references the matching groups:

print(m.expand(r"The total is \1 euros and \2 cents."))
# The total is 12 euros and 45 cents.

The escape sequences \1 and \2 are actually references to the matching groups of the match m. To make it easier to include the references, a raw string r"..." is used, otherwise the backslashes would have to be doubled.