Regex

REGEX

Official RE Doc

r"""RE
The special characters are:
    "."      Matches any character except a newline.
    "^"      Matches the start of the string.
    "$"      Matches the end of the string or just before the newline at
             the end of the string.
    "*"      Matches 0 or more (greedy) repetitions of the preceding RE.
             Greedy means that it will match as many repetitions as possible.
    "+"      Matches 1 or more (greedy) repetitions of the preceding RE.
    "?"      Matches 0 or 1 (greedy) of the preceding RE.
    *?,+?,?? Non-greedy versions of the previous three special characters.
    {m,n}    Matches from m to n repetitions of the preceding RE.
    {m,n}?   Non-greedy version of the above.
    "\\"     Either escapes special characters or signals a special sequence.
    []       Indicates a set of characters.
             A "^" as the first character indicates a complementing set.
    "|"      A|B, creates an RE that will match either A or B.
    (...)    Matches the RE inside the parentheses.
             The contents can be retrieved or matched later in the string.
    (?aiLmsux) Set the A, I, L, M, S, U, or X flag for the RE (see below).
    (?:...)  Non-grouping version of regular parentheses.
    (?P<name>...) The substring matched by the group is accessible by name.
    (?P=name)     Matches the text matched earlier by the group named name.
    (?#...)  A comment; ignored.
    (?=...)  Matches if ... matches next, but doesn't consume the string.
    (?!...)  Matches if ... doesn't match next.
    (?<=...) Matches if preceded by ... (must be fixed length).
    (?<!...) Matches if not preceded by ... (must be fixed length).
    (?(id/name)yes|no) Matches yes pattern if the group with id/name matched,
                       the (optional) no pattern otherwise.
The special sequences consist of "\\" and a character from the list
below.  If the ordinary character is not on the list, then the
resulting RE will match the second character.
    \number  Matches the contents of the group of the same number.
    \A       Matches only at the start of the string.
    \Z       Matches only at the end of the string.
    \b       Matches the empty string, but only at the start or end of a word.
    \B       Matches the empty string, but not at the start or end of a word.
    \d       Matches any decimal digit; equivalent to the set [0-9] in
             bytes patterns or string patterns with the ASCII flag.
             In string patterns without the ASCII flag, it will match the whole
             range of Unicode digits.
    \D       Matches any non-digit character; equivalent to [^\d].
    \s       Matches any whitespace character; equivalent to [ \t\n\r\f\v] in
             bytes patterns or string patterns with the ASCII flag.
             In string patterns without the ASCII flag, it will match the whole
             range of Unicode whitespace characters.
    \S       Matches any non-whitespace character; equivalent to [^\s].
    \w       Matches any alphanumeric character; equivalent to [a-zA-Z0-9_]
             in bytes patterns or string patterns with the ASCII flag.
             In string patterns without the ASCII flag, it will match the
             range of Unicode alphanumeric characters (letters plus digits
             plus underscore).
             With LOCALE, it will match the set [0-9_] plus characters defined
             as letters for the current locale.
    \W       Matches the complement of \w.
    \\       Matches a literal backslash.
This module exports the following functions:
    match     Match a regular expression pattern to the beginning of a string.
    fullmatch Match a regular expression pattern to all of a string.
    search    Search a string for the presence of a pattern.
    sub       Substitute occurrences of a pattern found in a string.
    subn      Same as sub, but also return the number of substitutions made.
    split     Split a string by the occurrences of a pattern.
    findall   Find all occurrences of a pattern in a string.
    finditer  Return an iterator yielding a Match object for each match.
    compile   Compile a pattern into a Pattern object.
    purge     Clear the regular expression cache.
    escape    Backslash all non-alphanumerics in a string.
Some of the functions in this module takes flags as optional parameters:
    A  ASCII       For string patterns, make \w, \W, \b, \B, \d, \D
                   match the corresponding ASCII character categories
                   (rather than the whole Unicode categories, which is the
                   default).
                   For bytes patterns, this flag is the only available
                   behaviour and needn't be specified.
    I  IGNORECASE  Perform case-insensitive matching.
    L  LOCALE      Make \w, \W, \b, \B, dependent on the current locale.
    M  MULTILINE   "^" matches the beginning of lines (after a newline)
                   as well as the string.
                   "$" matches the end of lines (before a newline) as well
                   as the end of the string.
    S  DOTALL      "." matches any character at all, including the newline.
    X  VERBOSE     Ignore whitespace and comments for nicer looking RE's.
    U  UNICODE     For compatibility only. Ignored for string patterns (it
                   is the default), and forbidden for bytes patterns.
This module also defines an exception 'error'.
"""

RegexOne and Medium


RegexOne

Medium

Other Reference


Characters

Character Legend Example Sample Match
\d Most engines: one digit from 0 to 9 file_\d\d file_25
\d .NET, Python 3: one Unicode digit in any script file_\d\d file_9੩
\w Most engines: “word character”: ASCII letter, digit or underscore \w-\w\w\w A-b_1
\w .Python 3: “word character”: Unicode letter, ideogram, digit, or underscore \w-\w\w\w 字-ま_۳
\w .NET: “word character”: Unicode letter, ideogram, digit, or connector \w-\w\w\w 字-ま‿۳
\s Most engines: “whitespace character”: space, tab, newline, carriage return, vertical tab a\sb\sc a b c
\s .NET, Python 3, JavaScript: “whitespace character”: any Unicode separator a\sb\sc a b c
\D One character that is not a digit as defined by your engine’s \d \D\D\D ABC
\W One character that is not a word character as defined by your engine’s \w \W\W\W\W\W *-+=)
\S One character that is not a whitespace character as defined by your engine’s \s \S\S\S\S Yoyo

Quantifiers

Quantifier Legend Example Sample Match
+ One or more Version \w-\w+ Version A-b1_1
{3} Exactly three times \D{3} ABC
{2,4} Two to four times \d{2,4} 156
{3,} Three or more times \w{3,} regex_tutorial
* Zero or more times ABC* AAACC
? Once or none plurals? plural

More Characters

Character Legend Example Sample Match
. Any character except line break a.c abc
. Any character except line break .* whatever, man.
**.** A period (special character: needs to be escaped by a ) a.c a.c
\ Escapes a special character .*+? $^/\ .*+? $^/\
\ Escapes a special character [{()}] [{()}]

Logic

Logic Legend Example Sample Match
| Alternation / OR operand 22|33 33
( … ) Capturing group A(nt|pple) Apple (captures “pple”)
\1 Contents of Group 1 r(\w)g\1x regex
\2 Contents of Group 2 (\d\d)+(\d\d)=\2+\1 12+65=65+12
(?: … ) Non-capturing group A(?:nt|pple) Apple

More White-Space

Character Legend Example Sample Match
\t Tab T\t\w{2} T ab
\r Carriage return character see below
\n Line feed character see below
\r\n Line separator on Windows AB\r\nCD AB CD
\N Perl, PCRE (C, PHP, R…): one character that is not a line break \N+ ABC
\h Perl, PCRE (C, PHP, R…), Java: one horizontal whitespace character: tab or Unicode space separator
\H One character that is not a horizontal whitespace
\v .NET, JavaScript, Python, Ruby: vertical tab
\v Perl, PCRE (C, PHP, R…), Java: one vertical whitespace character: line feed, carriage return, vertical tab, form feed, paragraph or line separator
\V Perl, PCRE (C, PHP, R…), Java: any character that is not a vertical whitespace
\R Perl, PCRE (C, PHP, R…), Java: one line break (carriage return + line feed pair, and all the characters matched by \v)

More Quantifiers

Quantifier Legend Example Sample Match
+ The + (one or more) is “greedy” \d+ 12345
? Makes quantifiers “lazy” \d+? 1 in 12345
* The * (zero or more) is “greedy” A* AAA
? Makes quantifiers “lazy” A*? empty in AAA
{2,4} Two to four times, “greedy” \w{2,4} abcd
? Makes quantifiers “lazy” \w{2,4}? ab in abcd

Character Classes

Character Legend Example Sample Match
[ … ] One of the characters in the brackets [AEIOU] One uppercase vowel
[ … ] One of the characters in the brackets T[ao]p Tap or Top
- Range indicator [a-z] One lowercase letter
[x-y] One of the characters in the range from x to y [A-Z]+ GREAT
[ … ] One of the characters in the brackets [AB1-5w-z] One of either: A,B,1,2,3,4,5,w,x,y,z
[x-y] One of the characters in the range from x to y [ -~]+ Characters in the printable section of the ASCII table.
[^x] One character that is not x [^a-z]{3} A1!
[^x-y] One of the characters not in the range from x to y [^ -~]+ Characters that are not in the printable section of the ASCII table.
[\d\D] One character that is a digit or a non-digit [\d\D]+ Any characters, inc- luding new lines, which the regular dot doesn’t match
[\x41] Matches the character at hexadecimal position 41 in the ASCII table, i.e. A [\x41-\x45]{3} ABE

Anchors and Boundaries

Anchor Legend Example Sample Match
^ Start of string or start of linedepending on multiline mode. (But when [^inside brackets], it means “not”) ^abc .* abc (line start)
$ End of string or end of linedepending on multiline mode. Many engine-dependent subtleties. .*? the end$ this is the end
\A Beginning of string (all major engines except JS) \Aabc[\d\D]* abc (string… …start)
\z Very end of the string Not available in Python and JS the end\z this is…\n…the end
\Z End of string or (except Python) before final line break Not available in JS the end\Z this is…\n…the end\n
\G Beginning of String or End of Previous Match .NET, Java, PCRE (C, PHP, R…), Perl, Ruby
\b Word boundary Most engines: position where one side only is an ASCII letter, digit or underscore Bob.*\bcat\b Bob ate the cat
\b Word boundary .NET, Java, Python 3, Ruby: position where one side only is a Unicode letter, digit or underscore Bob.*\b\кошка\b Bob ate the кошка
\B Not a word boundary c.\Bcat\B. copycats

POSIX Classes

Character Legend Example Sample Match
[:alpha:] PCRE (C, PHP, R…): ASCII letters A-Z and a-z [8[:alpha:]]+ WellDone88
[:alpha:] Ruby 2: Unicode letter or ideogram [[:alpha:]\d]+ кошка99
[:alnum:] PCRE (C, PHP, R…): ASCII digits and letters A-Z and a-z [[:alnum:]]{10} ABCDE12345
[:alnum:] Ruby 2: Unicode digit, letter or ideogram [[:alnum:]]{10} кошка90210
[:punct:] PCRE (C, PHP, R…): ASCII punctuation mark [[:punct:]]+ ?!.,:;
[:punct:] Ruby: Unicode punctuation mark [[:punct:]]+ ‽,:〽⁆

Inline Modifiers

None of these are supported in JavaScript. In Ruby, beware of

(?s)

and

(?m)

.

Modifier Legend Example Sample Match
(?i) Case-insensitive mode (except JavaScript) (?i)Monday monDAY
(?s) DOTALL mode (except JS and Ruby). The dot (.) matches new line characters (\r\n). Also known as “single-line mode” because the dot treats the entire input as a single line (?s)From A.*to Z From A to Z
(?m) Multiline mode (except Ruby and JS) ^ and $ match at the beginning and end of every line (?m)1\r\n^2$\r\n^3$ 1 2 3
(?m) In Ruby: the same as (?s) in other engines, i.e. DOTALL mode, i.e. dot matches line breaks (?m)From A.*to Z From A to Z
(?x) Free-Spacing Mode mode (except JavaScript). Also known as comment mode or whitespace mode (?x) # this is a # comment abc # write on multiple # lines [ ]d # spaces must be # in brackets abc d
(?n) .NET: named capture only Turns all (parentheses) into non-capture groups. To capture, use named groups.
(?d) Java: Unix linebreaks only The dot and the ^ and $ anchors are only affected by \n

Lookarounds

Lookaround Legend Example Sample Match
(?=…) Positive lookahead (?=\d{10})\d{5} 01234 in 0123456789
(?<=…) Positive lookbehind (?<=\d)cat cat in 1cat
(?!…) Negative lookahead (?!theatre)the\w+ theme
(?<!…) Negative lookbehind \w{3}(?<!mon)ster Munster

Character Class Operations

Class Operation Legend Example Sample Match
[…-[…]] .NET: character class subtraction. One character that is in those on the left, but not in the subtracted class. [a-z-[aeiou]] Any lowercase consonant
[…-[…]] .NET: character class subtraction. [\p{IsArabic}-[\D]] An Arabic character that is not a non-digit, i.e., an Arabic digit
[…&&[…]] Java, Ruby 2+: character class intersection. One character that is both in those on the left and in the && class. [\S&&[\D]] An non-whitespace character that is a non-digit.
[…&&[…]] Java, Ruby 2+: character class intersection. [\S&&[\D]&&[^a-zA-Z]] An non-whitespace character that a non-digit and not a letter.
[…&&[^…]] Java, Ruby 2+: character class subtraction is obtained by intersecting a class with a negated class [a-z&&[^aeiou]] An English lowercase letter that is not a vowel.
[…&&[^…]] Java, Ruby 2+: character class subtraction [\p{InArabic}&&[^\p{L}\p{N}]] An Arabic character that is not a letter or a number

Other Syntax

Syntax Legend Example Sample Match
\K Keep Out Perl, PCRE (C, PHP, R…), Python’s alternate regexengine, Ruby 2+: drop everything that was matched so far from the overall match to be returned prefix\K\d+ 12
\Q…\E Perl, PCRE (C, PHP, R…), Java: treat anything between the delimiters as a literal string. Useful to escape metacharacters. \Q(C++ ?)\E (C++ ?)

Curly Quotes

'”'.encode()

b'\xe2\x80\x9d'.decode()

'“'.encode()

b'\xe2\x80\x9c'.decode()

'‘'.encode()

b'\xe2\x80\x98'.decode()

'’'.encode()

b'\xe2\x80\x99'.decode()

u'Say (?:["“”])(.*)(?:["“”])'
# (?:["“”])    <-- Start non-capturing group, and match one of the three possible quote typesnot return it
# (.*)         <-- Start a capture group, match anything and return it
# (?:["“”])    <-- Stop matching the string until another quote is found

from unidecode import unidecode
line = unidecode('’')

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