Walrus Operator

What Does the Walrus Operator Do?

The walrus operator is also known as the assignment expression. It allows you to assign a value to a variable and use that variable in the same expression at the same time. This is something the regular = assignment operator cannot do.

Without the walrus operator you often find yourself writing two separate lines, one to assign a value and one to use it. The walrus operator lets you combine them into one.

A simple example without the walrus operator:

The same example using the walrus operator:

Both produce the same result but the walrus operator version is more concise. The value is assigned to n and immediately used in the condition in a single expression.

Walrus Operator with a while Loop

One of the most common and practical uses of the walrus operator is inside a while loop. Instead of assigning a value before the loop and updating it inside, you can do both in the loop condition itself.

The walrus operator assigns the user input to user_input and immediately evaluates whether it equals "quit" in the same line. Clean, concise and easy to read.

Walrus Operator with a List Comprehension

The walrus operator is also useful inside list comprehensions when you need to perform a calculation and use the result in both the condition and the output without calculating it twice.

Without the walrus operator you would either need to calculate the value twice or use a regular loop instead. The walrus operator keeps it in one clean expression.

Walrus Operator with a Function

You can also use the walrus operator to assign and check the result of a function call in a single line. This avoids calling the function twice just to store and then check the result.

Exercise 1: match / case (Python 3.10)

• Research: Python 3.10 introduced structural pattern matching using the match and case keywords. Find out how it works and how it compares to a chain of if, elif and else statements.
• Task: Create a variable command = "quit".
• Goal: Use match and case to print a different message for each of the following commands: "start", "stop", "quit" and a default case for anything else. Write a comment explaining how match / case differs from a chain of if / elif / else statements.

Exercise 2: Exception Groups (Python 3.11)

• Research: Python 3.11 introduced ExceptionGroup and the except* syntax which allows you to handle multiple exceptions at the same time. Find out how it works in the official documentation.
• Task: Create a simple ExceptionGroup containing a ValueError and a TypeError.
• Goal: Use except* to handle each exception type separately and print a message for each one. Write a comment explaining when this feature would be useful compared to a regular try / except block.

Exercise 3: Improved f-strings (Python 3.12)

• Research: Python 3.12 significantly improved f-strings allowing things that previously caused syntax errors. Find out what changed and what you can now do inside f-string curly braces that was not possible before.
• Task: Create a list scores = [45, 92, 78, 55, 88].
• Goal: Use the new f-string capabilities to print the maximum score, the minimum score and a sorted version of the list all inside a single f-string expression. Write a comment explaining what previously would have caused a syntax error that now works in 3.12.

Exercise 4: Type Parameter Syntax (Python 3.12)

• Research: Python 3.12 introduced a new cleaner syntax for generic type parameters using square brackets directly on a function or class definition. Find out how the new type statement works and how it simplifies type hints.
• Task: Write a simple generic function using the new type parameter syntax introduced in 3.12.
• Goal: Write a comment explaining what type hints are, why they are useful in larger codebases and how the new syntax in 3.12 improves on the previous approach.

Exercise 5: Your Choice

• Research: Browse the official Python What's New pages for versions 3.10 through to the latest release and find a feature that interests you that has not been covered in the previous exercises.
• Goal: Write a working example of the feature in VS Code. Write a comment explaining what the feature does, which version it was introduced in and why you found it interesting. Be prepared to explain it to someone who has never heard of it.