A regular expression (regex) is a text pattern used to find parts of a string. Python's re module is part of the standard library:

re.search() is a function with this signature:

• pattern — the regex to look for, written as a string.
• string — the text to scan.
• flags — optional; 0 means no special options (the ignore-case lesson covers them).
• It returns a match object for the first occurrence, or None when nothing matches.

A match object tells you what matched and where:

• .group() — the matched text.
• .start() — index of the first matched character, counted from 0.
• .end() — index after the last matched character, so the match is string[start:end].
• .span() — the tuple (start, end).

None is falsy, so if match: is the usual way to check whether something was found. re.search() stops at the first match and ignores the rest.

Coming from JavaScript? re.search(pattern, text) is close to text.match(pattern) for the first match, but Python returns a match object or None instead of null, and .group() replaces match[0].