findall, search, split, sub Function in Python 3.7

 

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)

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)

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())

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)

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)

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)

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)

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)

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

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 start with an upper case "S":

import re

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

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)

Example

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

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

import re

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

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