quick-ref-regex.md

Regular Expressions Quick Reference Table

Basic Metacharacters

Character	Description	Example	Matches
.	Any character except newline	a.b	"acb", "adb", "a3b", etc.
^	Start of string	^Hello	"Hello world" but not "Say Hello"
$	End of string	world$	"Hello world" but not "world class"
*	0 or more repetitions	ab*c	"ac", "abc", "abbc", etc.
+	1 or more repetitions	ab+c	"abc", "abbc", etc. but not "ac"
?	0 or 1 repetition	ab?c	"ac", "abc" but not "abbc"
{n}	Exactly n repetitions	a{3}	"aaa"
{m,n}	m to n repetitions	a{2,4}	"aa", "aaa", "aaaa"
{m,}	m or more repetitions	a{2,}	"aa", "aaa", "aaaa", etc.
\	Escape character	\.	Literal period "."
[]	Character class	[abc]	"a", "b", or "c"
|	Alternation (OR)	cat|dog	"cat" or "dog"
()	Grouping	(ab)+	"ab", "abab", etc.

Character Classes

Expression	Description	Equivalent
\d	Any digit	[0-9]
\D	Any non-digit	[^0-9]
\w	Any word character	[a-zA-Z0-9_]
\W	Any non-word character	[^a-zA-Z0-9_]
\s	Any whitespace	[ \t\n\r\f\v]
\S	Any non-whitespace	[^ \t\n\r\f\v]
[abc]	Any of listed characters	-
[^abc]	Any character except listed	-
[a-z]	Any character in range	-

Assertions

Expression	Description
(?=...)	Positive lookahead
(?!...)	Negative lookahead
(?<=...)	Positive lookbehind
(?<!...)	Negative lookbehind
\b	Word boundary
\B	Not a word boundary

Common Python Regex Functions

Function	Description
re.search(pattern, string)	Returns first match or None
re.match(pattern, string)	Matches at start of string
re.findall(pattern, string)	Returns all matches as list
re.finditer(pattern, string)	Returns iterator of match objects
re.sub(pattern, repl, string)	Substitutes matches with replacement
re.split(pattern, string)	Splits string by pattern
re.compile(pattern)	Compiles pattern for reuse

Common Patterns for Data Science

Task	Pattern	Example
Email	[\w.%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}	user@example.com
Phone (US)	\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}	(555) 123-4567
Date (ISO)	\d{4}-\d{2}-\d{2}	2023-10-15
URL	https?://[^\s/$.?#].[^\s]*	https://example.com
IP Address	\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b	192.168.1.1
Credit Card	\b\d{4}[-\s]?\d{4}[-\s]?\d{4}[-\s]?\d{4}\b	1234-5678-9012-3456
ZIP Code (US)	\b\d{5}(?:-\d{4})?\b	12345 or 12345-6789