Python String index()

index() Syntax

It's syntax is:

str.index(sub[, start[, end]] )

index() Parameters

The index() method takes three parameters:

• sub - substring to be searched in the string str.
• start and end(optional) - substring is searched within str[start:end]

index() Return Value

• If substring exists inside the string, it returns the lowest index in the string where substring is found.
• If substring doesn't exist inside the string, it raises a ValueError exception.

The index() method is similar to the find() method for strings.

The only difference is that find() method returns -1 if the substring is not found, whereas index() throws an exception.

Example 1: index() With Substring argument Only

Output

Substring 'is fun': 19

Traceback (most recent call last):
  File "<string>", line 6, in 
    result = sentence.index('Java')
ValueError: substring not found

Note: Index in Python starts from 0 and not 1. So the occurrence is 19 and not 20.

Example 2: index() With start and end Arguments

Output

15
17
Traceback (most recent call last):
  File "<string>", line 10, in 
    print(quote.index('fun', 7, 18))
ValueError: substring not found