ItsMyCode: Python String rindex()

The Python String rindex() method is a built-in function that returns the substring’s highest index (last occurrence) in a given string. If not found, it raises ValueError: substring not found exception.

In this article, we will learn about the Python string rindex() method with the help of examples.

rindex() Syntax

The Syntax of rindex() method is:

str.rindex(sub, start, end)

rindex() Parameters

The rindex() method can take three parameters.

• sub – substring that needs to be searched in the given string.
• start (optional) – starting position where the substring needs to be searched within the string
• end (optional) – ending position where the substring needs to be searched within the string

Note: If the start and end indexes are not provided, by default, it takes 0 as the starting index and str.length-1 as the end index

rindex() Return Value

The rindex() method returns an integer value, an index of a substring.

• If the substring is found in the given string, the rindex() method will return the highest index of the substring.
• If the substring is not found in the given string, it throws ValueError: substring not found exception

Difference between rindex() method and rfind() method

The rindex() method is similar to rfind() method. The only major difference is that the rfind() method returns -1 if the substring is not found in a given string, whereas the rindex() method will raise the ValueError: substring not found exception.

Example 1: Find the last occurence of a string in Python

The index in Python starts from 0 and not from 1. Hence in the below example the last occurence of the substring ‘Code‘ is found at index position 25.

text = 'ItsMyCode - Learn how to Code in Python '

# find the index of last  occurence of substring
output = text.rindex('Code')
print("The index of last  occurrence of 'Code' is:", output)

# find the index of character
output = text.rindex('-')
print("The index of last occurrence of '-' is:", output)

Output

The index of last  occurrence of 'Code' is: 25
The index of last occurrence of '-' is: 10

Example 2: If string is not found ValueError: substring not found exception

Here the substring ‘Hello’ is not found in the given string and hence Python interpreter raises ValueError: substring not found exception.

text = 'ItsMyCode - Learn how to Code in Python '

# find the index of last occurence of substring
output = text.index('Hello')
print("The index of last occurrence of 'Hello' is:", output)

Output

Traceback (most recent call last):
  File "C:\Personal\IJS\Code\main.py", line 4, in <module>
    output = text.index('Hello')
ValueError: substring not found

Example 3: Python String rindex() using start and end arguments

text = 'ItsMycode - code, coder, coders, coding  '

# find the index of last occurence of substring 'code'
output = text.rindex('code', 18)
print("The index of last occurrence of 'code' is:", output)

# find the index of character ','
output = text.rindex(',', 8, 20)
print("The index of last occurrence of ',' is:", output)

# find the index of substring 'de'
output = text.rindex('de', 10, -6)
print("The index of last occurrence of 'de' is:", output)

Output

The index of last occurrence of 'code' is: 25
The index of last occurrence of ',' is: 16
The index of last occurrence of 'de' is: 27

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