Python Programming for Biology: Bioinformatics and Beyond

Regular expression codes

The  following  table  summarises  a  subset  of  the  code  syntaxes  which  have  special

meanings  within  regular  expression  specifications.  Note  that  regular  expressions  also

accept the escaped control characters which are present in general Python strings, such as

\n \r \t \ etc.

Regexp

code

Meaning

.

Matches any character, except newline (unless in flag=re.DOTALL

mode).

^

Matches the beginning of a string, or the beginning of a line if

flag=re.MULTILINE.

$

Matches the end of a string.

*

Requires zero or more matches.

+

Requires one or more matches.

?

Requires zero or one match.

*?, +?, ??

As above, but matching minimally (non-greedy) before the next

term.

{n}

Requires exactly n number or matches.

---

{min,max}

Requires between min and max matches, inclusive.

{min,max}?

As above, but matching minimally (non-greedy) before the next

term.

[abc]

Matches a set of explicit characters. Control codes like ‘.’ and ‘+’

are treated literally.

[a-e]

Matches a set made with a consecutive range of characters, from a

to e, inclusive.

May be combined with explicit characters.

[^abc]

Matches the inverse character set, i.e. if the character is not a, b or

c.

a|b

Matches either specification a or b.

(expression)

Captures part of a match as a group which may be recalled.

(?…)

An extended system allowing more complex rules.

See

http://www.python.org

for full documentation.

\1, \2, …

\99

Recalls the match from a numbered group.

Can be used to repeat a match or include group contents in a

substitution.

\A

Matches the beginning of a string.

\b

Matches a word boundary; between a word (\w) and non-word

(\W) character.

Used to match the edges of a word without specifying what’s

outside.

\B

Matches a non-word boundary.

\d

Matches digit characters.

Equivalent to the set [0-9].

\D

Matches non-digit characters.

\s

Matches whitespace characters.

Equivalent to the set [ \n\r\t\v\f].

\S

Matches non-whitespace characters.

\w

Matches alphanumeric characters and underscore (‘word’

---

characters).

Equivalent to the set [0-9a-zA-Z_].

\W

Matches non-word characters.

\Z

Matches the end of string.