Regular Expression in Python

Regular Expression is also known as RegEx.It is also used for pattern matching and search pattern.

re is built-in package in python.

Syntax for importing re

import re

Searching for Pattern

import re
string='Python Programming SmallCode'
print("For First Search:")
s1=re.search("^P.*e$",string)
print(s1)
print("For Second Search:")
s2=re.search("^k.*t$",string)
print(s2)

Output

For First Search:
<re.Match object; span=(0, 28), match='Python Programming SmallCode'>
For Second Search:
None

Meta Character

S.No	break
.	It matches any character except newline.
{ }	It matches Exactly the specified number of occurrences
[ ]	It matches a set of characters.
^	It matches starting with character or string.
$	It matches ends with character or string.
*	It matches zero or more occurrence.
+	It matches one or more occurrence.

search() function

Search() fuction are used to search the sequence and return the number of occurrence.

Example

st="Python Programming by SmallCode"
print("For First Search:")
y = re.search("\s", st)
print(y)

Output

For First Search:
<re.Match object; span=(6, 7), match=' '>

findall() function

findall() fuction returns the list of all matches in any sequences and if there is no match then it return empty list.

Example

import re
string='Python Programming by SmallCode'
s1=re.findall("P",string)
print("Matched List 1:",s1)
s2=re.findall("SM",string)
print("Matched List 2:",s2)

Output

Matched List 1: ['P', 'P']
Matched List 2: []

sub() function

sub() replace the some character or string with some character or string.

Example

import re

string='Python Programming By SC'
s1=re.sub("SC","SmallCode",string)
print("After Replacing:",s1)

Output

After Replacing: Python Programming By SmallCode

split() function

split() function split the sequence and return in the form of list.

Example

import re
string='Python Programming By SmallCode'
s1=re.split(" ",string)
print("After spliting:",s1)

Output

After spliting: ['Python', 'Programming', 'By', 'SmallCode']

split with number of occurrence

split() function split according to number of occurrence.

Example

import re
string='Python Programming By SmallCode'
s1=re.split(" ",string,3)
print("After spliting:",s1)

Output

After spliting: ['Python', 'Programming', 'By', 'SmallCode']