07. Regular Expressions

Regular Expressions

A RegEx, or Regular Expression is a sequence of characters that forms a search pattern. RegEx can be used to check if a string contains the specified search pattern.

Python has a built-in package called re, which can be used to work with Regular Expressions. Import the re module:

When you have imported the re module, you can start using regular expressions:

For Example:
import re

#Check if the string starts with "The" and ends with "Spain":

TXT = "The rain in Spain"
x = re.search("The rain", TXT )

if (x):
     print("YES! We have a match!")
else:
    print("No match")

Output:
Yes! We have a match

Regular Expression Functions

findall()

The findall() function returns a list containing all matches.

For Example :

import re
str = "The rain in Spain"   #Return a list containing every occurrence of "ai":

x = re.findall("ai", str)
print(x)

Output

[‘ai’, ‘ai’]

search()

The search() function searches the string for a match, and returns a match object if there is a match. If there is more than one match, only the first occurrence of the match will be returned:

For Example :

import re
TXT = "The rain in Spain"

x = re.search('world', txt)

if x:
     print("pattern found inside the string")
else:
     print("pattern not found")

Output :
pattern not found

split()

The split() function returns a list where the string has been split at each match

For Example :

import re
TXT = "The rain in Spain"
x = re.split("\s", TXT)
print(x)

Output:
['The', 'rain', 'in', 'Spain']

sub()

The sub() function replaces the matches with the text of your choice

For Example :

import re
str = "The rain in Spain"
x = re.sub("\s", ",", str)
print(x)

Output:
The,rain,in,Spain