Python String index() Method

By Lenin Mishra

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Difference between index() and find() in Python

Similar to find() method in Python, the index() method finds the first occurence of a certain value.

If the value is not found, it raises a ValueError exception. The find() method in Python on the other hand, returns -1, if the value is not found.

The index() method is not case sensitive.

Syntax of index() method

string.index(value, start end)

value:	The value to search for(Required)
start:	The integer position to start the search. Default is 0.(Optional)
end:	The integer position to end the search. Default is the end of the string.(Optional)

Example 1

Code

str1 = "Pylenin loves Python"

print(str1.index("Python"))

Output

14

The substring Python occurs first time at position 14 in the string.

Example 2 - Check for case sensitivity

Code

str1 = "Pylenin loves Python"

print(str1.index("python"))

Output

ValueError: substring not found

Example 3 - Search for a non-existing string.

Code

str1 = "Pylenin loves Python"

print(str1.index("Apples"))

Output

ValueError: substring not found

Example 4 - Search a substring s1 in a specific portion of string s2.

Code

s2 = 'I like reading Pylenin blogs on Python'
s1 = 'Python'

# Search between position 10 and 20
try:
    print(s2.index(s1, 10, 20))
except Exception as e:
    print(e.__class__, e)

print(f"'{s1}' occurs at index {s2.index(s1)}")

Output

<class 'ValueError'> substring not found
'Python' occurs at index 32

As you can see, the substring Python occurs at index 32, but we are searching within the index 10 and 20.

Because, we are using a try-except block, ValueError exception is not being raised. Learn more about Python Exceptions and ways to handle them.

Check out other commonly used Python string methods.

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