Commonly used regular expression symbols

Reference from Web Scraping with Python , Ryan Mitchell

Symbols	Meaning	Example	Example Match
*	Matches the preceding character, subexpression, or bracketed character, 0 or more times	a*b*	aaaaaaaa,aaabbbbb, bbbbbb
+	Matches the preceding character, subexpression, or bracketed character,1 or more times	a+b+	aaaaaaaab, aaabbbbb, abbbbbb
[]	Matches any character within the brackets (i.e., “Pick any one of these things”)	[A-Z]*	APPLE, CAPITALS, QWERTY
()	A grouped subexpression (these are evaluated fi rst, in the “order of operations” of regular expressions)	(a*b)*	aaabaab, abaaab, ababaaaaab
{m, n}	Matches the preceding character, subexpression, or bracketed character between m and n times (inclusive)	a{2,3}b{2,3}	aabbb, aaabbb,aabb
[^]	Matches any single character that is not in the brackets	[^A-Z]*	apple,lowercase,qwerty
|	Matches any character, string of characters, or subexpression, separated by the “I” (note that this is a vertical bar, or “pipe,” not a capital “i”)	b(a|i|e)d	bad, bid, bed
.	Matches any single character (including symbols, numbers, a space, etc.)	b.d	bad, bzd, b$d, b d
^	Indicates that a character or subexpression occurs at the beginning of a string	^a	apple, asdf, a
\	An escape character (this allows you to use “special” characters as their literal meaning)	\. \| \\	. | \
$	Often used at the end of a regular expression, it means “match this up to the end of the string.” Without it, every regular expression has a defacto “.*” at the end of it, accepting strings where only the fi rst part of the string matches. This can be thougt of as analogous to the ^ symbol.	[A-Z]*[a-z]*$	ABCabc, zzzyx, Bob
?!	“Does not contain.” This odd pairing of symbols, immediately preceding a character (or regular expression), indicates that that character should not be found in that specific place in the larger string. This can be tricky to use; after all, the character might be found in a diff erent part of the string. If trying to eliminate a character entirely, use in conjunction with a ^ and $ at either end.	^((?![A-Z]).)*$	no-caps-here, $ymb0ls a4e f!ne