python

python string indexof - get index of a substring

We can get the index of a substring in a python string using the index() function. We pass the substring as a parameter in the index() function and it returns the index value.

full_str = "Devsheet"

result = full_str.index("vs")

print(result)

# -> 2

In the above code snippet:

1. Defined a string variable full_str that contains a string value.

2. Using String.index() method and passing substring 'vs' as a parameter to it to get the index of the substring.

3. Print the result.

If the substring could not be found in the string then it will throw ValueError: substring not found. For example, if we use the below code to get the index of substring vst.

full_str.index("vst")

The code will throw the error as 'vst' substring does not exist in the string 'Devsheet'.

Traceback (most recent call last):
  File "main.py", line 3, in <module>
    result = full_str.index("vst")
ValueError: substring not found

Use of String.find() function to get the index of a substring

You can use python exception handling or use the find() function to handle the exception - substring not found. It will return -1 if the substring does not exist inside the string.

full_str = "Devsheet"

result = full_str.find("vst")

print(result)

# -> -1

The code will not throw any exception if the substring cound not be found and return -1. If the substring exists inside the string then it will return the index of substring like index() function.

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