In Python, a KeyError is a type of exception error that happens when you try to access a key (in a dictionary) that doesn’t exist. It can interrupt your code execution and potentially crash your application. In this tutorial, we’ll learn how to handle this common error.

Step 1: Understanding KeyError

A KeyError is a built-in exception in Python that indicates that a key referenced in your program doesn’t exist. It most commonly happens when dealing with dictionaries. For example:

Output:

KeyError: 'Alice'

This causes a KeyError because “Alice” is not a key in the students dictionary.

Step 2: Using a Try/Except Block

Python exceptions can be handled using a try/except statement. The “try” is used before the part of the code where the error can occur. The “except” block then handles the error. Here is a basic example:

Output:

This key does not exist.

Step 3: Using the Dictionary ‘get()’ Method

Another method to handle KeyError in Python is by using the get() method of the dictionary. The get() function returns the value for the given key if exists in the dictionary. If not, it returns ‘None’ or a default value if provided.

Output:

This key does not exist.

Conclusion

KeyError is a common issue especially when working with dictionaries in Python. But it can be easily handled using try/except blocks or the more elegant dictionary get() method.

Handling these errors gracefully is a significant part of writing a robust, error-resistant Python program. After reading this tutorial, you should be now able to prevent KeyErrors from interrupting your Python programs.

Full Code

Here is the final code for handling KeyError in Python: