How to Find the Index of an Element in a List

Summary: in this tutorial, you’ll learn how to find the index of an element in a list.

To find the index of an element in a list, you use the index() function.

The following example defines a list of cities and uses the index() method to get the index of the element whose value is 'Mumbai':

cities = ['New York', 'Beijing', 'Cairo', 'Mumbai', 'Mexico']

result = cities.index('Mumbai')
print(result)
Code language: Python (python)

It returns 3 as expected.

However, if you attempt to find an element that doesn’t exist in the list using the index() function, you’ll get an error.

This example uses the index() function to find the Osaka city in the cities list:

cities = ['New York', 'Beijing', 'Cairo', 'Mumbai', 'Mexico']

result = cities.index('Osaka')
print(result)
Code language: Python (python)

Error:

ValueError: 'Osaka' is not in list
Code language: Python (python)

To fix this issue, you need to use the in operator.

The in operator returns True if a value is in the list. Otherwise, it returns False.

Before using the index() function, you can use the in operator to check if the element that you want to find is in the list. For example:

cities = ['New York', 'Beijing', 'Cairo', 'Mumbai', 'Mexico']
city = 'Osaka'

if city in cities:
    result = cities.index(city)
    print(f"The {city} has an index of {result}.")
else:
    print(f"{city} doesn't exist in the list.")
Code language: Python (python)

Output:

Osaka doesn't exist in the list.
Code language: Python (python)

Summary

• Use the in operator with the index() function to find if an element is in a list.