Regular Expressions

Build a pattern from a few readable pieces:

Form	Meaning
.	any character except a newline by default
^ / $	start / end anchors
[abc] / [^abc]	allowed / excluded character set
*, +, ?, {m,n}	repetition
(…) / (?:…)	capturing / non-capturing group
\b	word boundary in Python's re syntax

Use raw strings for Python patterns so Python string escaping does not obscure regex escaping:

import re

text = "Order A-104, order B-208"
codes = re.findall(r"\b[A-Z]-\d{3}\b", text)
updated = re.sub(r"(?i)\border\b", "item", text)
is_code = re.fullmatch(r"[A-Z]-\d{3}", "A-104") is not None

Choose the operation deliberately: search() finds the first match anywhere, fullmatch() requires the entire input, findall() collects matches, and sub() replaces them. Test representative matches, non-matches, empty input, Unicode, and unusually long input before using a pattern on untrusted data.

Regex syntax differs between Python, JavaScript, editors, and command-line tools. Treat the Python re documentation as authoritative only for Python; use RegExr as an interactive scratchpad, not as the specification for every engine.