Regex

Symbol Category Meaning / Description
. Wildcard Matches any single character except newline
\d Character class Matches any digit (same as [0-9])
\D Character class Matches any non-digit
\w Character class Matches any word character (letters, digits, underscore)
\W Character class Matches any non-word character
\s Character class Matches any whitespace (space, tab, newline)
\S Character class Matches any non-whitespace character
[...] Character set Matches any one character inside brackets
[^...] Negated set Matches any character not inside brackets
` ` Alternation
() Grouping Groups expressions, enables capturing or combining parts
(?:...) Non-capturing group Groups pattern but doesn’t capture it
(?P<name>...) Named group Captures a group with a name
\b Anchor Word boundary (between word and non-word character)
\B Anchor Not a word boundary
^ Anchor Matches the start of the string (or line with multiline flag)
$ Anchor Matches the end of the string (or line with multiline flag)
* Quantifier Matches 0 or more repetitions
+ Quantifier Matches 1 or more repetitions
? Quantifier Matches 0 or 1 (makes preceding token optional)
{n} Quantifier Matches exactly n repetitions
{n,} Quantifier Matches n or more repetitions
{n,m} Quantifier Matches between n and m repetitions
? after quant. Lazy modifier Makes quantifier non-greedy (match as little as possible)
(?=...) Lookahead (positive) Match if followed by pattern (doesn’t include it in result)
(?!...) Lookahead (negative) Match if not followed by pattern
(?<=...) Lookbehind (positive) Match if preceded by pattern
(?<!...) Lookbehind (negative) Match if not preceded by pattern
\\ Escape Escapes a special character (e.g., \. matches a literal dot)

Python re module

Method Purpose Parameters Returns Notes
match() Match pattern at the start of string pattern, string, flags=0 Match object or None Good for “does this string start with…”
search() Search anywhere in string pattern, string, flags=0 Match object or None Finds first occurrence
fullmatch() Match the entire string pattern, string, flags=0 Match object or None Use for strict validation
findall() Find all non-overlapping matches pattern, string, flags=0 List of strings or tuples Use finditer() for match objects instead
finditer() Iterate over all matches as objects pattern, string, flags=0 Iterator of Match objects Useful for position info, grouping, etc.
sub() Replace pattern with replacement string pattern, repl, string, count=0 New string Use for find-and-replace
subn() Like sub(), but also returns count pattern, repl, string, count=0 Tuple: (string, count) Great for auditing replacements
split() Split string by pattern pattern, string, maxsplit=0 List of strings Smarter than str.split()
compile() Compile pattern for reuse pattern, flags=0 Compiled pattern object Improves performance with repeated use
escape() Escape special regex chars in input string
Property / Method Description
.group() Returns the entire match (or a specific group if passed an index)
.groups() Returns a tuple of all captured groups (excluding named groups)
.groupdict() Returns a dictionary of all named capturing groups
.start() Returns the start index of the match
.end() Returns the end index (1 past the last character) of the match
.span() Returns a tuple (start, end) representing the range of the match
.pos The starting position of the search within the string
.endpos The ending position (limit) of the search
.re The regular expression object used for the match
.string The original string passed to re.search() or similar
.lastgroup The name of the last matched capturing group
.lastindex The index of the last matched capturing group (by number)

References