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The index() string method determines the index of the first occurrence of a particular string value within the invoked string object.

• Signature of index() method




# Signature of index method
 index(value)




Parameters	Description
value	This is a string value, which is searched in the invoked string and the method index() returns the first index of value(if found), otherwise the error i.e. ValueError is reported.








• Example of index() method


We are searching for the index of a particular value in a string object using index() method. If the searched value is found, its first index is returned.



# Python - Program to find a particular string value in a string.



# Creating a string
s1 = 'Let us learn Python'


# Finding the index of a value 'us' in the string
index1 = s1.index('us')

print('First Index of us in ',  s1 , ' : ' , index1)



# Finding the index of a value 'lea' in the string
index2 = s1.index('lea')

print('First Index of lea in ', s1 ,  ' : ', index2)



# Finding the index of a value 'Py' in the string
index3 = s1.index('Py')

print('First Index of Py in ', s1 ,  ' : ', index3)





Output is :




First Index of us in  Let us learn Python  :  4
First Index of lea in  Let us learn Python  :  7
First Index of Py in  Let us learn Python  :  13





Program Analysis



String is initialized with value Let us learn Python
• Index of the first occurrence of value us in the string object is found 4.
• Index of the first occurrence of value lea in the string object is found 1.
• Index of the first occurrence of value Py in the string object is found, hence 13 is returned.







• If the searched value is not found, the ValueError is reported


Here in this next example, we are searching for the index of a particular value in a string object using index() method. If the searched string is found, its first index is returned, otherwise the ValueError is reported at the runtime of the program.



# Python - Program to find a particular string value in a string.



# Creating a string
s1 = 'Let us learn Python'


# Finding the index of a value 'haha' in the string
index1 = s1.index('haha')

print('First Index of Py in ', s1 ,  ' : ', index1)





Output is :




Traceback (most recent call last):
  File "D:/Python Programs/index.py", line 10, in <module>
    index1 = s1.index('haha')
ValueError: substring not found






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• Method index() performs a case-sensitive search.

Both forms of index() method perform a case-sensitive search, whether it comes to the search of an index of a value in a string object.

# Python - Program to find a particular value in a String.


s1 = 'Let us Jazz and jam'
s2 = 'Live and let live'

index1 = s1.index('j')
index2 = s2.index('live')

print('First index of J in ', s1, ' : ', index1)
print('First index of live in ', s1, ' : ', index2)

Output is :

First index of J in  Let us Jazz and jam  :  7
First index of live in  Let us Jazz and jam  :  13

Program Analysis

First String is initialized with value Let us Jazz and jam, second String is initialized with value Live and let live.
• Index of the first occurrence of value lower case j in the first String object is found at index 5.
• Index of the first occurrence of value lower case live in the second String object is found at index 13.

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< String endswith() Method

String find() Method >

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