Python String index() Method
The index() method in Python is used to find the position of a specified substring within a given string. It is similar to the find() method but raises a ValueError if the substring is not found, while find() returns -1. This can be helpful when we want to ensure that the substring exists in the string before proceeding. Let’s see a simple use of index():
s = "Python programming"
p = s.index("prog")
print(p)
s = "Python programming"p = s.index("prog")print(p)Output
7
Explanation: index() method searches for the substring “prog” within “Python programming” and returns starting index 7.
Syntax of index()
s.index(substring, start=0, end=len(s))
Parameters:
- substring: The substring to locate within the string s.
- start (optional): The starting index for the search. Defaults to 0 if not provided.
- end (optional): The ending index for the search. If not provided, it defaults to the length of the string.
Return Type:
- Returns the lowest index of the substring if found in the given string.
- Raises a ValueError if the substring is not found in the specified range.
Example of index() Method
Let’s understand the use of index() with the help of some examples.
Example 1: Using index() with only substring argument
This code demonstrates how to find the index of a substring within a string using the index() method.
s = "Python programming is powerful"
p = s.index("programming")
print(p)
s = "Python programming is powerful"p = s.index("programming")print(p)Output
7
Explanation:
- Here, we only provide the substring argument “programming”.
- index() searches from the start of the string and finds “programming” at index 7, which it returns.
Example 2: Using index() with substring, start and end arguments
This code demonstrates how to find the index of a substring within a specific range of a string using the index() method with optional start and end parameters.
s = "Python programming is fun"
p = s.index("is", 10, 25)
print(p)
s = "Python programming is fun"p = s.index("is", 10, 25)print(p)Output
19
Explanation:
- We specify start=10 and end=25, so index() searches between these positions.
- It finds “is” at index 18 within this range and returns 18.
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