Regular Expression Examples in Python

Literal characters

Sr.No.	Example & Description
1	python Matches beginning of line.

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: [ \t\r\n\f]
5	\S Match nonwhitespace: [^ \t\r\n\f]
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>"

Grouping with Parentheses

Sr.No.	Example & Description
1	\D\d+ No group: + repeats \d
2	(\D\d)+ Grouped: + repeats \D\d pair
3	([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.

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 ?

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	Python\Z Match "Python" at the end of a string
5	\bPython\b Match "Python" at a word boundary
6	\brub\B \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.