How to Find Index in Python List

Last Updated on March 13, 2023 by Prepbytes

In python, a list is a data type or we can say a collection of values that are ordered and mutable. So when working with a list, Sometimes we need to find the index of a particular element. So in this section, we are going to discuss, how to find index of element in list python, Methods by which we can get index of element in list python.

Methods to Find Index of Element in Python List

In python, we have two methods to find index of element in list python:

1)Using index() Function to get Index of Element in Python List

The index() method is used to find the index of an element in a list. we will explore how to use the index() method to find the index of an element in a list in Python, with syntax and examples.

Syntax of index() functions:
The syntax for using the index() function:

list.index(element, start, end)

Parameters of index() function
Here are the parameters of the index () function :

• element: This is the required parameter or argument and it is the element that we want to find the index of. The data type of this element can be float, string, integer, or float.
• start (optional): It is an optional parameter, The start parameter specifies the index of the first element to start the search. The default value of start is 0, which means the search will start from the first element of the list.
• end (optional): It is also an optional parameter and this end parameter specifies the index of the last element to include in the search. The default value of end is the length of the list, which means the search will end at the end of the list.

Example 1 to find index of element in list python using the index method
Let’s take a look at an example to understand how to use the index() function to find the index of an element in a list.

Code Implementation

fruits = ['orange', 'banana', 'cherry', 'apple', 'mango']
index = fruits.index('orange')
print(index)

Output:

0

Explanation:
In the above example, we have defined a list called fruits that contains five elements. Now we have to find the index of the first occurrence of the element ‘orange’. So for this, we call the index() method on the list and pass ‘orange’ as the first argument. The method returns 0, which is the index of the first occurrence of ‘apple’ in the list.

Example 2 to find index of element in list python with start and end parameters
Let’s take another example where we specify the starting and ending indices of the search.

Code Implementation

fruits = ['apple', 'banana', 'cherry', 'apple', 'mango']
# Find the index of 'apple' starting from index 1 and ending 3
index = fruits.index('apple', 1, 4)
print(index)

Output:

3

Explanation:
In the preceding example, we specified a starting index of 1 and an ending index of 4. The ‘apple’ search is carried out from index 1 to index 3. The method returns the index of the second occurrence of ‘apple’ in the list, which is 3.

Example 3 to find index of element in list python when the element not present then what will index function return:
When an element is not present in the list and we use the index() function to find its index, a ValueError is raised. Here is an example:

# your code goes here

fruits = ['apple', 'banana', 'orange', 'grape']
try:
    index = fruits.index('mango')
    print(index)
except ValueError:
    print("The element is not present in the list")

Output:

The element is not present in the list

Explanation:
In the preceding example, we defined a list called fruits that does not contain the element’mango’. To find the index of mango,’ we used the index() method. Because’mango’ is not in the list, the index() method throws a ValueError, which is handled by a try-except block. The except block displays a message indicating that the element is not in the list.

2) Using a for Loop to get Index of Element in Python List

We can also use a for loop to get the index of an element in a list. Here’s an example:

# your code goes here

fruits = ['apple', 'banana', 'orange', 'grape', 'banana']
search_element = 'banana'
indices = []
for i in range(len(fruits)):
    if fruits[i] == search_element:
        indices.append(i)
print("The indices of", search_element, "in the list are:", indices)

Output:

The indices of banana in the list are: [1, 4]

Explanation
In the above example, we defined a list of string called fruits, which contains multiple occurrences of the string element ‘banana’. So here we have to find the indices where
‘banana’ exist. So we make a variable search_element and set it to ‘banana,’ the element whose indices we want to find. After this, We’ve also made an empty list called indices to hold the search element’s indices in the list. We then use a for loop to iterate through the list, checking if each element is equal to the search element. If it is, we add the index of that element to the list of indices.

Finally, we print out the indices of the search element in the list using the indices list. Note that the for loop method will find all occurrences of the search element in the list and return their indices, while the index() method will only return the index of the first occurrence of the search element.

Conclusion
In this article we have discussed the index function, syntax of the index function, and parameters of the index function, We have discussed how we can get the index of a specific element in a list using the index function and if the element is not present in the list , then index function raise value error , we can use index function to locate the position of an element and at last we use for loop to get the index of an element

Frequently Asked Questions(FAQs)

Here are some FAQs on how to find index of element in list python:

Q1: What will happen if the element is not present in the list?
A: If the given item is not in the list, the index() method will give a value error.

Q2: Can we find the index of an element in a list that occurs multiple times?
A: Yes, we can find the index of an element in a list multiple times, but the output of the index() function will only give the index of the first occurrence of the element in the list.

Q3: Can we use the index method with other data types besides lists?
A: No, the index function or method is only specific to the list data type in Python.

Q4: Can we modify or update the list while searching for an element or item using the index() method?
A: Yes, we can modify the list while searching for an element using the index() method. However, if the index of the element is removed or modified from the list but it can affect the accuracy of the index() method.