Python 3 RE Cheat Sheet

py3_re_cheat_sheet.md

Regex Cheat Sheet (Python re)

Basics

Pattern	Meaning
.	Any character except newline (unless re.DOTALL)
^	Start of string (or start of line if re.MULTILINE)
$	End of string (or end of line if re.MULTILINE)
\A	Start of string (ignores MULTILINE)
\Z	End of string (ignores MULTILINE)
\b	Word boundary
\B	Not a word boundary
\\	Escape special character

Character Classes

Pattern	Meaning
[abc]	Any of a, b, or c
[^abc]	Any character except a, b, or c
[a-z]	Range: any lowercase letter
\d	Digit [0-9]
\D	Not a digit
\w	Word character [a-zA-Z0-9_]
\W	Not a word character
\s	Whitespace (space, tab, newline, etc.)
\S	Not whitespace

Quantifiers

Pattern	Meaning
*	0 or more
+	1 or more
?	0 or 1 (optional)
{n}	Exactly n
{n,}	At least n
{n,m}	Between n and m
*?, +?, ??, {n,m}?	Non-greedy versions

Groups

Pattern	Meaning
(abc)	Capture group
(?:abc)	Non-capturing group
(?P<name>abc)	Named group
(?P=name)	Backreference by name
\1, \2	Backreference by group number
(?=abc)	Positive lookahead
(?!abc)	Negative lookahead
(?<=abc)	Positive lookbehind (fixed-width)
(?<!abc)	Negative lookbehind (fixed-width)

Alternation

Pattern	Meaning
`a	b`

Flags (inline and with re module)

Flag	Inline	Meaning
re.IGNORECASE	(?i)	Case-insensitive
re.MULTILINE	(?m)	^ and $ match line boundaries
re.DOTALL	(?s)	. matches newlines
re.VERBOSE	(?x)	Allow whitespace/comments in pattern
re.ASCII	(?a)	\w, \d, \s match only ASCII
re.LOCALE	(?L)	Deprecated, locale-dependent classes
re.UNICODE	(?u)	Unicode matching (default in Python 3)

Escapes

Escape	Meaning
\n, \r, \t	Newline, carriage return, tab
\xhh	Hex byte
\uhhhh	Unicode code point (16-bit)
\Uhhhhhhhh	Unicode code point (32-bit)
\ooo	Octal value

Useful Functions in re

Function	Use
re.match(pat, s)	Match at start
re.fullmatch(pat, s)	Match whole string
re.search(pat, s)	First match anywhere
re.findall(pat, s)	Return all matches (list of strings/tuples)
re.finditer(pat, s)	Iterator of match objects
re.sub(pat, repl, s)	Replace matches
re.split(pat, s)	Split by regex
re.compile(pat, flags)	Precompile regex