Python

Regular Expression

• Python regular expression module available in re package.

• Special characters used in regular expression, -

Character	Description	Example pattern code	Example match
\d	A digit	file_\d\d	file_24
\w	Aplhanumeric (Also include underscore characters in match)	\w-\w\w\w	A-b_1
\s	Whilespace	a\sb\s\c	a b c
\D	A non digit	\D\D\D\D	aBcD
\W	Non-alphanumeric	\W\W\W\W\W	*_+=)
\S	Non-whitespace	\S\S\S\S	Yoyo

• Occurences related special characters, -

Character	Description	Example pattern code	Example match
+	Occurs one or more times	Version \w-\w+	Version A-B_1
{3}	Occurs three times	\D{3}	123
{2,4}	Occurs 2 to 4 times	\d{2,4}	123
{3,}	Occurs 3 or more times	\w{3,}	sdaw3rfwe4
*	Occurs zero or more times	ABC*	AAACCC
?	Occur Once or None	plurals?	plural

• Condition based regular expression characters, -

Character	Description	Example pattern code	Example match
pipe sign	OR condition in regular expression	r’cat	dog’	Statement 1: This is a dog! Statement 2: This is a cat!
. (wild char)	period sign indicate wild char for get given position	r’…at’	Statement : The cat in the hat went splat Result will be - [‘e cat’, ‘e hat’, ‘splat’]
^ (power sign)	First occurence should match with pattern	r’^\d’	Statement : 2 is Number. Result will be - [2]
$ (dollar sign)	Last occurence should match with pattern	r’$\d’	Statement : The Number is 2 Result will be - [2]

IN keyword example:

Input:

my_var = 'bhushan' in 'bhushan is my name'
print(my_var)

Output:

True

Simple Expression search function example:

Input:

import re
my_statement = "Agent Hitman has phone Number (999)-999-9999 You can call at any time on this phone number!!!"
pattern = 'NO PATTERN SET'
re.search(pattern, my_statement)

Output: No output will be available. If we try to print output it will be None type

Input:

import re
my_statement = "Agent Hitman has phone Number (999)-999-9999 You can call at any time on this phone number!!!"

#return first find object from statement.
pattern = 'phone'
re.search(pattern, my_statement)

Output:

<re.Match object; span=(17, 22), match='phone'>

Methods from Match object

Method	Description
span()	return start and end attribute of first match in tuple
start()	return start index
end()	return end index
group()	return search text

Input:

import re
my_statement = "Agent Hitman has phone Number (999)-999-9999 You can call at any time on this phone number!!!"

#return first find object from statement.
pattern = 'phone'
match = re.search(pattern, my_statement)
print(match.span())
print(match.start())
print(match.end())
print(match.group())

Output:

(17, 22)
17
22
phone

Simple Expression findall function example:

Input:

import re
my_statement = "Agent Hitman has phone Number (999)-999-9999 You can call at any time on this phone number!!!"

#return first find object from statement.
pattern = 'phone'
match_list = re.findall(pattern, my_statement)
print(f'Total search count : {len(match_list)}')
print(f'Search Text        : {match_list}')
for (index, match) in enumerate(match_list):
    print(f'Search Number {index}')
    print(f'\t\t found at: {match}')

Output:

Total search count : 2
Search Text        : ['phone', 'phone']
Search Number 0
		 found at: phone
Search Number 1
		 found at: phone

Simple Expression finditer function example:

Input:

import re
my_statement = "Agent Hitman has phone Number (999)-999-9999 You can call at any time on this phone number!!!"

#return first find object from statement.
pattern = 'phone'
for match in re.finditer(pattern, my_statement):
    print(f'{match.group()} found at: {match.start()}, {match.end()}')

Output:

phone found at: 17, 22
phone found at: 78, 83

Note: finditer function iterate over match object while findall function return only occurences

Regular Expression search function example:

Input:

import re
my_statement = "Agent Hitman has phone Number (999)-999-9999 You can call at any time on this phone number!!!"

#return first find object from statement.
pattern = r'\W\d{3}\W-\d{3}-\d{4}'
for match in re.finditer(pattern, my_statement):
    print(f'{match.group()} found at: {match.start()}, {match.end()}')

Output:

(999)-999-9999 found at: 30, 44

Regular Expression compile and search function example:

compile function from re package compile regular expression and divide it into groups. For this purpose it uses open and closing brackets.

Input:

import re
my_statement = "Agent Hitman has phone Number (999)-999-9999 You can call at any time on this phone number!!!"

#return first find object from statement.
pattern = re.compile('\W(\d{3})\W-(\d{3})-(\d{4})') #Each open and closing bracket represent group.
result = re.search(pattern, my_statement)
print(result.span())
print(f'Group 1 {result.group(1)}')
print(f'Group 2 {result.group(2)}')
print(f'Group 3 {result.group(3)}')
print(f'Group 4 {result.group(4)}') # ==> Generate Error as there is no 4th group available

Output:

(30, 44)
Group 1 999
Group 2 999
Group 3 9999

Multiple Regular Expression with OR condition (PIPE separator) example:

Input:

import re
friend_name = 'Harshal'
statement = f'{friend_name} is my friend and He is my best friend and his contact detail is 838-009-3898'
pattern = re.compile('Abhay|Harshal|Sanjay|Abhijeet')
search_result = re.search(pattern, statement)
if search_result != None:
    print(f'Result found with start index {search_result.start()} and end index {search_result.end()}')
    print(f'Available friend is {search_result.group()}')
else:
    print('No result found!')

Output:

Result found with start index 0 and end index 7
Available friend is Harshal

Wild char Regular Expression (period sign) example:

Input:

import re
friend_name = 'Sanket'
statement = f'{friend_name} is my friend and He is my good friend and his contact detail is 838-009-3898'
pattern = re.compile('my......friend')
search_result = re.search(pattern, statement)
if search_result != None:
    print(f'Result found with start index {search_result.start()} and end index {search_result.end()}')
    print(f'Available friend is {search_result.group()}')
else:
    print('No result found!')

Output:

Result found with start index 30 and end index 44
Available friend is my good friend

Exclusion operation with Regular Expression example:

import re
#exclusion syntax with the help of regular expression
statement = 'there are 3 numbers 34 inside 5 this sentence'
pattern = r'[^\d]'  # Generate list of characters from above statement
pattern = r'[^\d]+' # Generate list of words which gets separated with number
re.findall(pattern, statement)

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