Python Regex Cheat Sheet

Posted : admin On 1/29/2022

The Python RegEx Cheat Sheet for Budding Programmers Get Creative When Using Python Learning Python's regular expressions is a big step towards becoming a better Python programmer, but that's just one of the few things you need to do. However, playing around with its syntaxes and getting creative with them polishes your coding skill. Regex Cheat Sheet. GitHub Gist: instantly share code, notes, and snippets.

Ds-cheatsheets / Python / Dataquest / python-regular-expressions-cheat-sheet.pdf Go to file Go to file T; Go to line L; Copy path Copy permalink. Cannot retrieve. Pythex is a quick way to test your Python regular expressions. Try writing one or test the example. Match result: Match captures: Regular expression cheatsheet Special characters escape special characters. Matches any character ^ matches beginning of string $ matches end of string 5b-d.

Above visualization is a screenshot created usingdebuggexfor the patternr'bpar(en ro)?tb'


Python Regex Cheat Sheet Answers

From docs.python: re:

A regular expression (or RE) specifies a set of strings that matches it; the functions in this module let you check if a particular string matches a given regular expression

This blog post gives an overview and examples of regular expression syntax as implemented by the re built-in module (Python 3.8+). Assume ASCII character set unless otherwise specified. This post is an excerpt from my Python re(gex)? book.

Elements that define a regular expression🔗

AnchorsDescription
Arestricts the match to the start of string
Zrestricts the match to the end of string
^restricts the match to the start of line
$restricts the match to the end of line
nnewline character is used as line separator
re.MULTILINE or re.Mflag to treat input as multiline string
brestricts the match to the start/end of words
word characters: alphabets, digits, underscore
Bmatches wherever b doesn't match

^, $ and are metacharacters in the above table, as these characters have special meaning. Prefix a character to remove the special meaning and match such characters literally. For example, ^ will match a ^ character instead of acting as an anchor.

FeatureDescription
multiple RE combined as conditional OR
each alternative can have independent anchors
(RE)group pattern(s), also a capturing group
a(b c)d is same as abd acd
(?:RE)non-capturing group
(?P<name>pat)named capture group
.Match any character except the newline character n
[]Character class, matches one character among many
Greedy QuantifiersDescription
*Match zero or more times
+Match one or more times
?Match zero or one times
{m,n}Match m to n times (inclusive)
{m,}Match at least m times
{,n}Match up to n times (including 0 times)
{n}Match exactly n times
pat1.*pat2any number of characters between pat1 and pat2
pat1.*pat2 pat2.*pat1match both pat1 and pat2 in any order

Greedy here means that the above quantifiers will match as much as possible that'll also honor the overall RE. Appending a ? to greedy quantifiers makes them non-greedy, i.e. match as minimally as possible. Quantifiers can be applied to literal characters, groups, backreferences and character classes.

Character classDescription
[aeiou]Match any vowel
[^aeiou]^ inverts selection, so this matches any consonant
[a-f]- defines a range, so this matches any of abcdef characters
dMatch a digit, same as [0-9]
DMatch non-digit, same as [^0-9] or [^d]
wMatch word character, same as [a-zA-Z0-9_]
WMatch non-word character, same as [^a-zA-Z0-9_] or [^w]
sMatch whitespace character, same as [ tnrfv]
SMatch non-whitespace character, same as [^ tnrfv] or [^s]
LookaroundsDescription
lookaroundscustom assertions, zero-width like anchors
(?!pat)negative lookahead assertion
(?<!pat)negative lookbehind assertion
(?=pat)positive lookahead assertion
(?<=pat)positive lookbehind assertion
(?!pat1)(?=pat2)multiple assertions can be specified in any order
as they mark a matching location without consuming characters
((?!pat).)*Negate a grouping, similar to negated character class
FlagsDescription
re.IGNORECASE or re.Iflag to ignore case
re.DOTALL or re.Sallow . metacharacter to match newline character
flags=re.S re.Imultiple flags can be combined using operator
re.MULTILINE or re.Mallow ^ and $ anchors to match line wise
re.VERBOSE or re.Xallows to use literal whitespaces for aligning purposes
and to add comments after the # character
escape spaces and # if needed as part of actual RE
re.ASCII or re.Amatch only ASCII characters for b, w, d, s
and their opposites, applicable only for Unicode patterns
re.LOCALE or re.Luse locale settings for byte patterns and 8-bit locales
(?#comment)another way to add comments, not a flag
(?flags:pat)inline flags only for this pat, overrides flags argument
flags is i for re.I, s for re.S, etc, except L for re.L
(?-flags:pat)negate flags only for this pat
(?flags-flags:pat)apply and negate particular flags only for this pat
(?flags)apply flags for whole RE, can be used only at start of RE
anchors if any, should be specified after (?flags)
Regex
Matched portionDescription
re.Match objectdetails like matched portions, location, etc
m[0] or m.group(0)entire matched portion of re.Match object m
m[n] or m.group(n)matched portion of nth capture group
m.groups()tuple of all the capture groups' matched portions
m.span()start and end+1 index of entire matched portion
pass a number to get span of that particular capture group
can also use m.start() and m.end()
Nbackreference, gives matched portion of Nth capture group
applies to both search and replacement sections
possible values: 1, 2 up to 99 provided no more digits
g<N>backreference, gives matched portion of Nth capture group
possible values: g<0>, g<1>, etc (not limited to 99)
g<0> refers to entire matched portion
(?P<name>pat)named capture group
refer as 'name' in re.Match object
refer as (?P=name) in search section
refer as g<name> in replacement section
groupdictmethod applied on a re.Match object
gives named capture group portions as a dict

0 and 100 onwards are considered as octal values, hence cannot be used as backreferences.

re module functions🔗

Regular Expression Cheat Sheet

FunctionDescription
re.searchCheck if given pattern is present anywhere in input string
Output is a re.Match object, usable in conditional expressions
r-strings preferred to define RE
Use byte pattern for byte input
Python also maintains a small cache of recent RE
re.fullmatchensures pattern matches the entire input string
re.compileCompile a pattern for reuse, outputs re.Pattern object
re.subsearch and replace
re.sub(r'pat', f, s)function f with re.Match object as argument
re.escapeautomatically escape all metacharacters
re.splitsplit a string based on RE
text matched by the groups will be part of the output
portion matched by pattern outside group won't be in output
re.findallreturns all the matches as a list
if 1 capture group is used, only its matches are returned
1+, each element will be tuple of capture groups
portion matched by pattern outside group won't be in output
re.finditeriterator with re.Match object for each match
re.subngives tuple of modified string and number of substitutions

The function definitions are given below:

Re Cheat Sheet


Regular expression examples🔗

As a good practice, always use raw strings to construct RE, unless other formats are required. This will avoid clash of special meaning of backslash character between RE and normal quoted strings.

  • examples for re.search
  • difference between string and line anchors
  • examples for re.findall

Python Regex Cheat Sheet For Beginners

  • examples for re.split
  • backreferencing within search pattern
  • working with matched portions
  • examples for re.finditer
  • examples for re.sub
  • backreferencing in replacement section

Python Regex Cheat Sheet Datacamp

  • using functions in replacement section of re.sub
  • examples for lookarounds
  • examples for re.compile

Python Regex Cheat Sheet Free

Regular expressions can be compiled using re.compile function, which gives back a re.Pattern object. The top level re module functions are all available as methods for this object. Compiling a regular expression helps if the RE has to be used in multiple places or called upon multiple times inside a loop (speed benefit). By default, Python maintains a small list of recently used RE, so the speed benefit doesn't apply for trivial use cases.


Python re(gex)? book🔗

Visit my repo Python re(gex)? for details about the book I wrote on Python regular expressions. The ebook uses plenty of examples to explain the concepts from the very beginning and step by step introduces more advanced concepts. The book also covers the third party module regex. The cheatsheet and examples presented in this post are based on contents of this book.

Use this leanpub link for a discounted price.