Regulary expressions in Python

Import the python built-in re module.
import re

import re

word = 'word_123 !'
match = re.fullmatch(r'.*', word)
print(bool(match))
# result: True

.* means any character, any number of times

---

1. Meta characters and special sequences
2. Functions of module re

---

1. Meta characters and special sequences

Meta characters

char	Description	Example	Matches
.	Matches any single character (except newline).	a.b	acb, a1b, a#b
^	Matches the start of the string.	^Start	Start of the sentence
$	Matches the end of the string.	End$	This is the End
*	Matches zero or more occurrences of the preceding element.	ab*c	ac, abc, abbbc
+	Matches one or more occurrences of the preceding element.	ab+c	abc, abbbc, but not ac
?	Matches zero or one occurrence of the preceding element (optional/lazy).	colou?r	color, colour
{m,n}	Matches at least m and at most n occurrences of the preceding element.	a{2,3}	aa, aaa
()	Groups elements together and creates a capturing group.	(abc)+	abc, abcabc
[]	Defines a character set, matching any single character contained within the brackets.	[aeiou]	a, e, i, o, or u
\	Escapes the following character, treating it literally or giving special meaning (e.g., \d).	\$100	$100

Special sequences

Sequence	Meaning	Simpler Example	Matches
\d	Matches any digit (0-9).	\d\d	12, 05, 99
\D	Matches any non-digit character.	\D+	Hello, ?!@, (a space)
\w	Matches any word character (letters, numbers, underscore, except symbols like !?,& ).	\w+	user_name, File1, _test
\W	Matches any non-word character (punctuation, space, symbol).	\W	!, @, #, (a space)
\s	Matches any whitespace character (space, tab, newline, etc.).	\s	A space (), a tab (\t), a newline (\n)
\S	Matches any non-whitespace character.	\S+	word!, 123, (text)

2. Functions of module re

re.fullmatch - checks for a match against the entire string
re.match - checks for a match only at the beginning (start) of the string

import re

word = '123_word !'
match = re.fullmatch(r'\d+', word)
print(match)
# result: None
# The entire word doesn't match the pattern

import re

word = '123_word !'
match = re.match(r'\d+', word)
print(match)
# result: <re.Match object; span=(0, 3), match='123'>
# The chars in the index span 0,3 of the beginning of the string match the pattern

word2 = 'word_123 !'
match = re.match(r'\d+', word2)
print(match)
# result: None

re.findall() - finds and returns all matching occurrences in a list

import re

word = 'word_123 !'
match = re.findall(r'\d+', word)
print(match)
# result: 123

split - splits a string wherever the pattern matches

import re

word = 'Words, words , Words'
match = re.split(r'\W+', word)
print(match)
# result: ['Words', 'words', 'Words']
# W - non-word

wor2 = 'On 12th Jan 2016, at 11:02 AM'
match = re.split(r'\d+', word2)
print(match)
# result: ['On ', 'th Jan ', ', at ', ':', ' AM']
# split the string by numbers