The index() function in python helps to return the position or index of the given substring in the string. If the searched substring is not found, it will raise an exception. Here we can also provide starting and ending point of the search through the string.
cstr.index(sub[, start[, end]] ) #where start & end should be integers
The index() function takes three parameters. If the start and end index is not provide searching will start from zero indexes and up to the end of the string. This method is similar to the find() method, the difference is that find() will return -1 if the searched substring is not found whereas an index() method throws an exception.
| Parameter | Description | Required / Optional |
|---|---|---|
| sub | substring to be searched in the string str | Required |
| start | start searching from this index | Optional |
| end | search the substring up to this index | Optional |
The output of this method should be an integer value indicating the position of the substring. If more than one occurrence of the substring is found, it will return the first occurrence only.
| Input | Return Value |
|---|---|
| if substring | index of substring |
| if no substring | ValueError exception |
string = 'Python is very easy to learn.'
result = string.index('very easy')
print("Substring 'very easy':", result)
result = string.index('Php')
print("Substring 'php':", result)
Output:
Substring 'very easy': 10 Traceback (most recent call last): File "", line 6, in result = string.index('Php') ValueError: substring not found
string = 'Python is very easy to learn.'
# Substring is searched in 'very'
print(string.index('very', 6))
# Substring is searched in 'easy '
print(string.index('easy', 5, 10))
# Substring is searched in 'to'
print(string.index('to', 15, 23))
Output:
10 Traceback (most recent call last): File "", line 7, in print(quote.index('easy', 5, 10)) ValueError: substring not found 20
