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.

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