What is the use of import re in python?

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.

RegEx Module

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

Import the re module:

RegEx in Python

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

Example

Search the string to see if it starts with "The" and ends with "Spain":

import re

txt = "The rain in Spain"
x = re.search("^The.*Spain$", txt)

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RegEx Functions

The re module offers a set of functions that allows us to search a string for a match:

Metacharacters

Metacharacters are characters with a special meaning:

Special Sequences

A special sequence is a \ followed by one of the characters in the list below, and has a special meaning:

Sets

A set is a set of characters inside a pair of square brackets [] with a special meaning:

The findall() Function

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

Example

Print a list of all matches:

import re

txt = "The rain in Spain"
x = re.findall("ai", txt)
print(x)

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The list contains the matches in the order they are found.

If no matches are found, an empty list is returned:

Example

Return an empty list if no match was found:

import re

txt = "The rain in Spain"
x = re.findall("Portugal", txt)
print(x)

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The search() Function

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:

Example

Search for the first white-space character in the string:

import re

txt = "The rain in Spain"
x = re.search("\s", txt)

print("The first white-space character is located in position:", x.start())

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If no matches are found, the value None is returned:

Example

Make a search that returns no match:

import re

txt = "The rain in Spain"
x = re.search("Portugal", txt)
print(x)

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The split() Function

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

Example

Split at each white-space character:

import re

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

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You can control the number of occurrences by specifying the maxsplit parameter:

Example

Split the string only at the first occurrence:

import re

txt = "The rain in Spain"
x = re.split("\s", txt, 1)
print(x)

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The sub() Function

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

Example

Replace every white-space character with the number 9:

import re

txt = "The rain in Spain"
x = re.sub("\s", "9", txt)
print(x)

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You can control the number of replacements by specifying the count parameter:

Example

Replace the first 2 occurrences:

import re

txt = "The rain in Spain"
x = re.sub("\s", "9", txt, 2)
print(x)

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Match Object

A Match Object is an object containing information about the search and the result.

Note: If there is no match, the value None will be returned, instead of the Match Object.

Example

Do a search that will return a Match Object:

import re

txt = "The rain in Spain"
x = re.search("ai", txt)
print(x) #this will print an object

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The Match object has properties and methods used to retrieve information about the search, and the result:

.span() returns a tuple containing the start-, and end positions of the match.
.string returns the string passed into the function
.group() returns the part of the string where there was a match

Example

Print the position (start- and end-position) of the first match occurrence.

The regular expression looks for any words that starts with an upper case "S":

import re

txt = "The rain in Spain"
x = re.search(r"\bS\w+", txt)
print(x.span())

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Example

Print the string passed into the function:

import re

txt = "The rain in Spain"
x = re.search(r"\bS\w+", txt)
print(x.string)

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Example

Print the part of the string where there was a match.

The regular expression looks for any words that starts with an upper case "S":

import re

txt = "The rain in Spain"
x = re.search(r"\bS\w+", txt)
print(x.group())

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Note: If there is no match, the value None will be returned, instead of the Match Object.

What is the purpose of using re?

What is re method in Python?

How do you add Re in Python?

What does re match () return?