Python - Check if an element is in a list

Python lists are quite versatile and can store a wide range of data in a sequential manner. It might be handy to know if an element belongs to a list or not. For example, you are a librarian at a public library, a person wants to check whether a book is available or not. Fortunately, you maintain a record of books available in the library as a python list and can quickly check this. In this tutorial, we will look at how to check whether an element is present in a python list or not.

How to check if an element is present in a list?

The best way to check if an element is in a python list is to use the membership operator in. The following is the syntax:

# here ls is a list of values
a in ls

The above expression returns a boolean value, True if a is present in the list ls and False if its not.

There are other methods as well to check for an element’s presence in a list but the above is probably the most simple and a considerably fast method. Let’s look at some examples to demonstrate its the usage.

# list of books
available_books = ["1984", "Animal Farm", "Dracula", "Moby Dick", "The Great Gatsby"]
# check if element in list
"Annabel" in available_books

Output:

False

We get False as the output since the element “Annabel” was not present in the list “available_books”. Let’s now check for a book that is present in the list.

# list of books
available_books = ["1984", "Animal Farm", "Dracula", "Moby Dick", "The Great Gatsby"]
# check if element in list
"Animal Farm" in available_books

Output:

True

You can see we get True as the output since the element “Animal Farm” is present in the list “available_books”.

📚 Data Science Programs By Skill Level

Introductory ⭐

Intermediate ⭐⭐⭐

Advanced ⭐⭐⭐⭐⭐

🔎 Find Data Science Programs 👨‍💻 111,889 already enrolled

Disclaimer: Data Science Parichay is reader supported. When you purchase a course through a link on this site, we may earn a small commission at no additional cost to you. Earned commissions help support this website and its team of writers.

Since lists are ordered, you can also get the index of the element you’re looking for using the list index() function. For example, let’s find the index of the above element in the list “available_books”.

# get the index of element
if "Animal Farm" in available_books:
    print(available_books.index("Animal Farm"))

Output:

We get 1 as the output. That is, the book “Animal Farm” is present at the 1st index (starting from 0).

If you’re not interested in the index and want to further speed up your code, you can first convert the list to a set and then check for the element in it using the in operator.

# check if element in set
"Animal Farm" in set(available_books)

Output:

True

We get True as the output since the element is present in the set.

For more on operators in python, refer to our comprehensive tutorial covering a wide range of operators used in python.

Subscribe to our newsletter for more informative guides and tutorials.
We do not spam and you can opt out any time.

Tutorials on python lists:

Author

Piyush Raj

Piyush is a data professional passionate about using data to understand things better and make informed decisions. He has experience working as a Data Scientist in the consulting domain and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects.

View all posts