Regular Expression Patterns

Following lists the regular expression syntax that is available in Python.

Pattern	Description
^	match beginning of the line.
$	match end of line.
.	match any single character except ' '.
[...]	match any single character in brackets.
re*	match 0 or more occurrences of preceding expression
re+	match 1 or more occurrences of preceding expression
re?	match 0 or 1 occurrence of preceding expression.
re{n}	match exactly n number of occurrences of preceding expression.
1...9	match n-th grouped sub-expression.
(re)	Groups regular expressions and remembers matched text.

Examples

# <
ESCAPE_RE = r'\(.)'

# *emphasis*
EMPHASIS_RE = r'(*)([^*]+)2'

# **strong**
STRONG_RE = r'(*{2}|_{2})(.+?)2'

# ***strongem*** or ***em*strong**
EM_STRONG_RE = r'(*|_)2{2}(.+?)2(.*?)2{2}'

# ***strong**em*
STRONG_EM_RE = r'(*|_)2{2}(.+?)2{2}(.*?)2'

# _smart_emphasis_
SMART_EMPHASIS_RE = r'(?<!w)(_)(?!_)(.+?)(?<!_)2(?!w)'

# _emphasis_
EMPHASIS_2_RE = r'(_)(.+?)2'

# [text](url) or [text](<url>) or [text](url "title")
LINK_RE = NOIMG + BRK + 
    r'''(s*(<.*?>|((?:(?:(.*?))|[^()]))*?)s*((['"])(.*?)12s*)?)'''

# ![alttxt](http://x.com/) or ![alttxt](<http://x.com/>)
IMAGE_LINK_RE = r'!' + BRK + r's*(s*(<.*?>|([^")s]+s*"[^"]*"|[^)s]*))s*)'

# [Google][3]
REFERENCE_RE = NOIMG + BRK + r's?[([^]]*)]'

# [Google]
SHORT_REF_RE = NOIMG + r'[([^]]+)]'