Index Function In Python: Complete Explanation With Examples

Index function in Python is very helpful when we have a lot of data which can be arranged in a serial manner. In Python we can use a variety of data structures and predefined methods which can hold different types of data in an organised manner.

When you have a list of students for registration of swimming class and the third student from the top cancelled their registration, then how will you remove them from the list. This is the exact place where you will need an index function in Python. In this blog, we will learn more about how to use the index() method.

Table of Contents

Index Function in Python Syntax & Parameters

The index function in Python consists of element, start and end parameters inside. It can be used with a list, tuple or string to search the index value of a particular element.

list.index(element, start, end)

Here, are the parameters of the Index() function in Python.

Element is the item you want to search for in the list. It is mandatory to declare what you are searching for in the list.
Start is the index to start searching for the element. It is optional and you can skip this part.
End is the last index up to which you want to search for the element. It is also optional to tell the value of end in the code.

The Index() Function in Python

The index function in Python returns the position of the data element in a given list or string. The index() method is used to return the index of the specified element in the list. Let us understand it using a simple example below.

fruits = [‘apple’, ‘banana’, ‘cherry’, ‘banana’, ‘orange’]

position = fruits.index(‘banana’)

print(“The first ‘banana’ is at index:”, position)

We need to find the element “banana” in the given list which we can easily complete using the index() method to find the position of the banana in the list.

Return Type In Index() Function In Python

In Python, list or string index() returns the index of a given element. If the value is not found in the list then you will get a valueError in the return value.

Remember that when you are using the index function in Python, then it will only return the first occurrence of the matching element.

text = “Hello, world!”

# Find the index of the first occurrence of ‘o’

index_o = text.index(‘o’)

print(“The first ‘o’ is at index:”, index_o)

You will find the ‘o’ character at the index 4 as an output on the screen. The return types are mainly integers.

What Is Index Function In Python?

The Index function in Python refers to a method of accessing the index of a specific element in a list or string. In Python, indexing starts at 0th index by default. For example, if you are accessing a string “Ankit” then the letter “A” is at 0 index, “n” is at 1 index, “k” is at 2 index, and so on.

This is a built-in function in Python which can help you find the exact position of an element in a list. If the given value which you are searching for is not present in the list, then it will return a “ValueError”. Suppose we have a list with numbers present inside i,e. [ 10, 20, 30, 40, 50, 60] and you are searching the element at list.index(7) then it will return a “ValueError”.

Examples of Index Function In Python

Let us look at some of the major examples where we can use the index() function.

1. Write a program to find the number 3 with start parameter as 2 using the index function in Python.

In this example, we have to find the index of number 3 located in the list. Also, for a twist we have been given the starting index from where the search for the index number starts. We will embed the starting index after the element we are searching in the list. We will get the index as 3 in the list.

numbers = [5, 3, 7, 3, 9, 3]

print(numbers.index(3, 2))

2. Write a Python program to find a message i,e. Hello World in between a given starting and ending occurrence.

In this Python program we have to find a character ‘o’ in the list from the string “hello world”. We will start searching the string from the first index i,e. 0 index. The ‘o’ character in the string is located at 4th index of the string.

message = “hello world”

print(message.index(‘o’))

3. Write a Python Program to find substring in a given quote using the index function in Python.

In this Python program we are looking for a word in a phrase i,e. “power” in the phrase i,e. Knowledge is power. We will start searching from the 0th index and keep on looking until we find the “power” first index. The index is the 13 number in the phrase.

quote = “Knowledge is power.”

print(quote.index(“power”))

4. Write a Python program to handle errors when an element is not found in a list.

In this Python program we will have a list where we can print the index of the lion and if “lion” is not present in the list then you can generate a custom valueError where you will display that “element is not found in the list”.

animals = [‘cat’, ‘dog’, ‘rabbit’]

try:

print(animals.index(‘lion’))

except ValueError:

print(“Element not found in the list.”)

5. Write a program to find the index of a Dictionary with a specific value.

# List of student records

students = [

{‘id’: 1, ‘name’: ‘Alice’},

{‘id’: 2, ‘name’: ‘Bob’},

{‘id’: 3, ‘name’: ‘Charlie’},

{‘id’: 4, ‘name’: ‘Diana’}

]

names = [student[‘name’] for student in students]

index_of_charlie = names.index(‘Charlie’)

print(“Charlie is at index:”, index_of_charlie)

print(“Charlie’s full record:”, students[index_of_charlie])

In this example we have a dictionary with keys and values stored in a variable students. We have to find the index of a student named “Charlie”. Let us use the Index function in Python to find the index of Charlie.

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