Python Regex - re.MatchObject.start() and re.MatchObject.end() functions

In this article, we are going to see re.MatchObject.start() and re.MatchObject.end() regex methods.

re.MatchObject.start() 

This method returns the first index of the substring matched by group.

Syntax: re.MatchObject.start([group])

Parameter:

• group: (optional) group defaults to zero (meaning the whole matched substring). Return -1 if group exists but did not contribute to the match. 

Return: Index of start of the substring matched by group.

AttributeError: If a matching pattern is not found then it raise AttributeError.

re.MatchObject.end()

This method returns the last index of the substring matched by group.

Syntax: re.MatchObject.end([group])

Parameter:

• group: (optional) group defaults to zero (meaning the whole matched substring). Return -1 if group exists but did not contribute to the match. 

Return: Index of end of the substring matched by group.

AttributeError: If a matching pattern is not found then it raise AttributeError.

Consider the below example:

Example 1:

import re

# getting the match of the string
search_pattern = re.search('\d+',
                           '1234')

""" 
d: stands for integer
+: means a consecutive set of 
characters satisfying a condition. 
Hence d+ will match consecutive 
integer string 
"""

print(search_pattern.string)

print(search_pattern.start())

print(search_pattern.end())

Output:

1234
0
4

Let's understand the code. In the third line of the code we use the re.search() method to find a match in the given string('1234') the 'd' indicates that we are searching for a numeric character and the '+' indicates that we are searching for continuous numeric characters in the given string. The result we get is a re.MatchObject which is stored in search_pattern. If you print search_pattern.string you will get '1234' as output. 

In the above example, the search_pattern.start() returns value 0 as the index of the first element of the matched string in the given string is 0 and the search_pattern.end() returns 4 that is the end index after the end of the string. 

Example 2:

import re

# getting the match of the string
search_pattern = re.search('\d+',
                           'abcd')
""" 
d: stands for integer
+: means a consecutive set of characters 
satisfying a condition. 
Hence d+ will match consecutive 
integer string 
"""

print(search_pattern.start())

print(search_pattern.end())

Output:

Traceback (most recent call last):
  File "/home/4f904f4b53a786e10faa03122533f96b.py", line 13, in 
    print(search_pattern.start())
AttributeError: 'NoneType' object has no attribute 'start'