Python String index() method example

In this source code example, we will demonstrate how to use the Python string index() method to get the index of a substring in a string.

Basically, we use the index() to get the lowest index of a substring within a string.

Python String index() method

The string index() method returns the lowest index of a substring in a string.

The following shows the syntax of the index() method:

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

The index() method has three parameters:

• sub is the substring to search for in the str.
• start and end parameters are interpreted as in the slice notation str[start:end]. The slice specifies where to look for the substring sub. Both start and end parameters are optional.

Python String index() method examples

The following example shows how to use the index() method to find the substring 'Code' in the string 'Source Code Examples.':

s = 'Source Code Examples'
position = s.index('Code')

print(position)

Output:

7

The following example uses the index() method to find the substring 'Code' in the string 'Source Code Examples' within the slice str[1:]:

s = 'Source Code Examples, Source'
position = s.index('Source', 1)

print(position)

Output:

22

The following example raises a ValueError because the substring 'Python' doesn’t exist in the string 'Source Code Examples':

s = 'Source Code Examples'
position = s.index('Python')
print(position)

Output:

Traceback (most recent call last):
  File "main.py", line 2, in <module>
    position = s.index('Python')
ValueError: substring not found

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