Regular Expressions — Pattern Matching

import re

Basic patterns:

. — any character

\d — digit, \w — word char, \s — whitespace

^ — start, $ — end

* — 0 or more, + — 1 or more, ? — 0 or 1

{3} — exactly 3, {2,5} — 2 to 5

Key functions:

text = "My phone is 555-867-5309"

re.search(r"\d{3}-\d{3}-\d{4}", text)  # first match
re.findall(r"\d+", text)   # all numbers: ['555','867','5309']
re.sub(r"\d", "X", text)   # replace digits with X
re.match(r"My", text)      # only at start

Groups:

match = re.search(r"(\d{3})-(\d{3})-(\d{4})", text)
if match:
    area = match.group(1)   # "555"
    full = match.group(0)   # entire match

Email validation example:

pattern = r"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$"
if re.match(pattern, email):
    print("Valid email")

Reference:

Wikipedia: Regular Expression

https://en.wikipedia.org/wiki/Regular_expression