Python 3 Regex Cheat Sheet

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Python 3 Regex Cheat Sheet Pdf
Python 3 Cheat Sheet Pdf

Python 3 Advanced Tutorial

Python 3 Useful Resources

Anyone can forget how to make character classes for a regex, slice a list or do a for loop. This cheat sheet tries to provide a basic reference for beginner and advanced developers, lower the entry barrier for newcomers and help veterans refresh the old tricks. REGEX CHEAT SHEET Python, PHP, and Perl Supported Metacharacters Metacharacters Meaning a Alert b Backspace Newline r Carriage return f Form feed.

Selected Reading

A regular expression is a special sequence of characters that helps you match or find other strings or sets of strings, using a specialized syntax held in a pattern. Regular expressions are widely used in UNIX world.

The module re provides full support for Perl-like regular expressions in Python. The re module raises the exception re.error if an error occurs while compiling or using a regular expression.

We would cover two important functions, which would be used to handle regular expressions. Nevertheless, a small thing first: There are various characters, which would have special meaning when they are used in regular expression. To avoid any confusion while dealing with regular expressions, we would use Raw Strings as r'expression'.

Basic patterns that match single chars

Sr.No.	Expression & Matches
1	a, X, 9, < ordinary characters just match themselves exactly.
2	. (a period) matches any single character except newline 'n'
3	w matches a 'word' character: a letter or digit or underbar [a-zA-Z0-9_].
4	W matches any non-word character.
5	Apple store offers. b boundary between word and non-word
6	s matches a single whitespace character -- space, newline, return, tab
7	Apk on chrome os. S matches any non-whitespace character.
8	t, n, r tab, newline, return
9	d decimal digit [0-9]
10	^ matches start of the string
11	$ match the end of the string Apps for stores.
12	inhibit the 'specialness' of a character.

Compilation flags

Compilation flags let you modify some aspects of how regular expressions work. Flags are available in the re module under two names, a long name such as IGNORECASE and a short, one-letter form such as I.

Sr.No.	Flag & Meaning
1	ASCII, A Makes several escapes like w, b, s and d match only on ASCII characters with the respective property.
2	DOTALL, S Make, match any character, including newlines
3	IGNORECASE, I Do case-insensitive matches
4	LOCALE, L Do a locale-aware match
5	MULTILINE, M Multi-line matching, affecting ^ and $
6	VERBOSE, X (for ‘extended’) Enable verbose REs, which can be organized more cleanly and understandably

The match Function

This function attempts to match RE pattern to string with optional flags.

Here is the syntax for this function −

Here is the description of the parameters −

Sr.No.	Parameter & Description
1	pattern This is the regular expression to be matched.
2	string This is the string, which would be searched to match the pattern at the beginning of string.
3	flags You can specify different flags using bitwise OR (\|). These are modifiers, which are listed in the table below.

Sr.No.

Parameter & Description

pattern

This is the regular expression to be matched.

string

This is the string, which would be searched to match the pattern at the beginning of string.

flags

You can specify different flags using bitwise OR (|). These are modifiers, which are listed in the table below.

The re.match function returns a match object on success, None on failure. We usegroup(num) or groups() function of match object to get matched expression.

Sr.No.	Match Object Method & Description
1	group(num = 0) This method returns entire match (or specific subgroup num)
2	groups() This method returns all matching subgroups in a tuple (empty if there weren't any)

Sr.No.

Match Object Method & Description

group(num = 0)

This method returns entire match (or specific subgroup num)

groups()

This method returns all matching subgroups in a tuple (empty if there weren't any)

Example

When the above code is executed, it produces the following result −

The search Function

This function searches for first occurrence of RE pattern within string with optional flags.

Here is the syntax for this function −

Here is the description of the parameters −

Sr.No.	Parameter & Description
1	pattern This is the regular expression to be matched.
2	string This is the string, which would be searched to match the pattern anywhere in the string.
3	flags You can specify different flags using bitwise OR (\|). These are modifiers, which are listed in the table below.

Sr.No.

Parameter & Description

pattern

This is the regular expression to be matched.

string

This is the string, which would be searched to match the pattern anywhere in the string.

flags

You can specify different flags using bitwise OR (|). These are modifiers, which are listed in the table below.

The re.search function returns a match object on success, none on failure. We use group(num) or groups() function of match object to get the matched expression.

Sr.No.	Match Object Method & Description
1	group(num = 0) This method returns entire match (or specific subgroup num)
2	groups() This method returns all matching subgroups in a tuple (empty if there weren't any)

Sr.No.

Match Object Method & Description

group(num = 0)

This method returns entire match (or specific subgroup num)

groups()

This method returns all matching subgroups in a tuple (empty if there weren't any)

Example

When the above code is executed, it produces the following result −

Matching Versus Searching

Python offers two different primitive operations based on regular expressions: match checks for a match only at the beginning of the string, while search checks for a match anywhere in the string (this is what Perl does by default).

Example

When the above code is executed, it produces the following result −

Search and Replace

One of the most important re methods that use regular expressions is sub.

Syntax

This method replaces all occurrences of the RE pattern in string with repl, substituting all occurrences unless max is provided. This method returns modified string.

Example

When the above code is executed, it produces the following result −

Regular Expression Modifiers: Option Flags

Regular expression literals may include an optional modifier to control various aspects of matching. The modifiers are specified as an optional flag. You can provide multiple modifiers using exclusive OR (|), as shown previously and may be represented by one of these −

Sr.No.	Modifier & Description
1	re.I Performs case-insensitive matching.
2	re.L Interprets words according to the current locale. This interpretation affects the alphabetic group (w and W), as well as word boundary behavior (b and B).
3	re.M Makes $ match the end of a line (not just the end of the string) and makes ^ match the start of any line (not just the start of the string).
4	re.S Makes a period (dot) match any character, including a newline.
5	re.U Interprets letters according to the Unicode character set. This flag affects the behavior of w, W, b, B.
6	re.X Permits 'cuter' regular expression syntax. It ignores whitespace (except inside a set [] or when escaped by a backslash) and treats unescaped # as a comment marker.

Regular Expression Patterns

Except for the control characters, (+ ? . * ^ $ ( ) [ ] { } | ), all characters match themselves. You can escape a control character by preceding it with a backslash.

The following table lists the regular expression syntax that is available in Python −

Here is the list of regular expression syntax in Python.

Sr.No.	Parameter & Description
1	^ Matches beginning of line.
2	$ Matches end of line.
3	. Matches any single character except newline. Using m option allows it to match newline as well.
4	[..] Matches any single character in brackets.
5	[^..] Matches any single character not in brackets
6	re* Matches 0 or more occurrences of preceding expression.
7	re+ Matches 1 or more occurrence of preceding expression.
8	re? Matches 0 or 1 occurrence of preceding expression.
9	re{ n} Matches exactly n number of occurrences of preceding expression.
10	re{ n,} Matches n or more occurrences of preceding expression.
11	re{ n, m} Matches at least n and at most m occurrences of preceding expression.
12	a\|b Matches either a or b.
13	(re) Groups regular expressions and remembers matched text.
14	(?imx) Temporarily toggles on i, m, or x options within a regular expression. If in parentheses, only that area is affected.
15	(?-imx) Temporarily toggles off i, m, or x options within a regular expression. If in parentheses, only that area is affected.
16	(?: re) Groups regular expressions without remembering matched text.
17	(?imx: re) Temporarily toggles on i, m, or x options within parentheses.
18	(?-imx: re) Temporarily toggles off i, m, or x options within parentheses.
19	(?#..) Comment.
20	(?= re) Specifies position using a pattern. Does not have a range.
21	(?! re) Specifies position using pattern negation. Does not have a range.
22	(?> re) Matches independent pattern without backtracking.
23	w Matches word characters.
24	W Matches nonword characters.
25	s Matches whitespace. Equivalent to [tnrf].
26	S Matches nonwhitespace.
27	d Matches digits. Equivalent to [0-9].
28	D Matches nondigits.
29	A Matches beginning of string.
30	Z Matches end of string. If a newline exists, it matches just before newline.
31	z Matches end of string.
32	G Matches point where last match finished.
33	b Matches word boundaries when outside brackets. Matches backspace (0x08) when inside brackets.
34	B Matches non-word boundaries.
35	n, t, etc. Matches newlines, carriage returns, tabs, etc.
36	1..9 Matches nth grouped subexpression.
37	10 Matches nth grouped subexpression if it matched already. Otherwise refers to the octal representation of a character code.

Regular Expression Examples

Literal characters

Sr.No.	Example & Description
1	python Match 'python'.

Character classes

Sr.No.	Example & Description
1	[Pp]ython Match 'Python' or 'python'
2	rub[ye] Match 'ruby' or 'rube'
3	[aeiou] Match any one lowercase vowel
4	[0-9] Match any digit; same as [0123456789]
5	[a-z] Match any lowercase ASCII letter
6	[A-Z] Match any uppercase ASCII letter
7	[a-zA-Z0-9] Match any of the above
8	[^aeiou] Match anything other than a lowercase vowel
9	[^0-9] Match anything other than a digit

Special Character Classes

Sr.No.	Example & Description
1	. Match any character except newline
2	d Match a digit: [0-9]
3	D Match a nondigit: [^0-9]
4	s Match a whitespace character: [ trnf]
5	S Match nonwhitespace: [^ trnf]
6	w Match a single word character: [A-Za-z0-9_]
7	W Match a nonword character: [^A-Za-z0-9_]

Repetition Cases

Sr.No.	Example & Description
1	ruby? Match 'rub' or 'ruby': the y is optional
2	ruby* Match 'rub' plus 0 or more ys
3	ruby+ Match 'rub' plus 1 or more ys
4	d{3} Match exactly 3 digits
5	d{3,} Match 3 or more digits
6	d{3,5} Match 3, 4, or 5 digits

Nongreedy repetition

This matches the smallest number of repetitions −

Sr.No.	Example & Description
1	*<.>** Greedy repetition: matches '<python>perl>'
2	*<.?>** Nongreedy: matches '<python>' in '<python>perl>'

Sr.No.

Example & Description

<.*>

Greedy repetition: matches '<python>perl>'

<.*?>

Nongreedy: matches '<python>' in '<python>perl>'

Grouping with Parentheses

Sr.No.	Example & Description
1	Dd+ No group: + repeats d
2	(Dd)+ Grouped: + repeats Dd pair
3	([Pp]ython(,)?)+ Match 'Python', 'Python, python, python', etc.

Sr.No.

Example & Description

Dd+

No group: + repeats d

(Dd)+

Grouped: + repeats Dd pair

([Pp]ython(,)?)+

Match 'Python', 'Python, python, python', etc.

Backreferences

This matches a previously matched group again −

Sr.No.	Example & Description
1	([Pp])ython&1ails Match python&pails or Python&Pails
2	*(['])[^1]1** Single or double-quoted string. 1 matches whatever the 1st group matched. 2 matches whatever the 2nd group matched, etc.

Sr.No.

Example & Description

([Pp])ython&1ails

Match python&pails or Python&Pails

(['])[^1]*1

Single or double-quoted string. 1 matches whatever the 1st group matched. 2 matches whatever the 2nd group matched, etc.

Alternatives

Sr.No.	Example & Description
1	python\|perl Match 'python' or 'perl'
2	rub(y\|le) Match 'ruby' or 'ruble'
3	Python(!+\|?) 'Python' followed by one or more ! or one ?

Sr.No.

Example & Description

python|perl

Match 'python' or 'perl'

rub(y|le)

Match 'ruby' or 'ruble'

Python(!+|?)

'Python' followed by one or more ! or one ?

Anchors

This needs to specify match position.

Sr.No.	Example & Description
1	^Python Match 'Python' at the start of a string or internal line
2	Python$ Match 'Python' at the end of a string or line
3	APython Match 'Python' at the start of a string
4	PythonZ Match 'Python' at the end of a string
5	bPythonb Match 'Python' at a word boundary
6	brubB B is nonword boundary: match 'rub' in 'rube' and 'ruby' but not alone
7	Python(?=!) Match 'Python', if followed by an exclamation point.
8	Python(?!!) Match 'Python', if not followed by an exclamation point.

Special Syntax with Parentheses

Sr.No.	Example & Description
1	R(?#comment) Matches 'R'. All the rest is a comment
2	R(?i)uby Case-insensitive while matching 'uby'
3	R(?i:uby) Same as above
4	rub(?:y\|le)) Group only without creating 1 backreference

The tables below are a reference to basic regex. While reading the rest of the site, when in doubt, you can always come back and look here. (It you want a bookmark, here's a direct link to the regex reference tables). I encourage you to print the tables so you have a cheat sheet on your desk for quick reference.
The tables are not exhaustive, for two reasons. First, every regex flavor is different, and I didn't want to crowd the page with overly exotic syntax. For a full reference to the particular regex flavors you'll be using, it's always best to go straight to the source. In fact, for some regex engines (such as Perl, PCRE, Java and .NET) you may want to check once a year, as their creators often introduce new features.
The other reason the tables are not exhaustive is that I wanted them to serve as a quick introduction to regex. If you are a complete beginner, you should get a firm grasp of basic regex syntax just by reading the examples in the tables. I tried to introduce features in a logical order and to keep out oddities that I've never seen in actual use, such as the 'bell character'. With these tables as a jumping board, you will be able to advance to mastery by exploring the other pages on the site.

How to use the tables

The tables are meant to serve as an accelerated regex course, and they are meant to be read slowly, one line at a time. On each line, in the leftmost column, you will find a new element of regex syntax. The next column, 'Legend', explains what the element means (or encodes) in the regex syntax. The next two columns work hand in hand: the 'Example' column gives a valid regular expression that uses the element, and the 'Sample Match' column presents a text string that could be matched by the regular expression.
You can read the tables online, of course, but if you suffer from even the mildest case of online-ADD (attention deficit disorder), like most of us… Well then, I highly recommend you print them out. You'll be able to study them slowly, and to use them as a cheat sheet later, when you are reading the rest of the site or experimenting with your own regular expressions.
Enjoy!
If you overdose, make sure not to miss the next page, which comes back down to Earth and talks about some really cool stuff: The 1001 ways to use Regex.

Regex Accelerated Course and Cheat Sheet

For easy navigation, here are some jumping points to various sections of the page:
✽ Characters
✽ Quantifiers
✽ More Characters
✽ Logic
✽ More White-Space
✽ More Quantifiers
✽ Character Classes
✽ Anchors and Boundaries
✽ POSIX Classes
✽ Inline Modifiers
✽ Lookarounds
✽ Character Class Operations
✽ Other Syntax

(direct link)

Characters

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

(direct link)

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

(direct link)

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	[{()}]	[{()}]

(direct link)

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)g1x	regex
2	Contents of Group 2	(dd)+(dd)=2+1	12+65=65+12
(?: … )	Non-capturing group	A(?:nt\|pple)	Apple

(direct link)

More White-Space

Character	Legend	Example	Sample Match
t	Tab	Ttw{2}	T ab
r	Carriage return character	see below
n	Line feed character	see below
rn	Line separator on Windows	ABrnCD	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)

(direct link)