3 minute read

Introduced in Python 3.8, the walrus operator is a game-changing assignment operator that allows us to assign a value to a variable as part of an expression. This nifty tool can be particularly useful in situations where you need to perform an operation based on the value of an expression, such as in loops or conditional statements. By reducing the number of lines of code, it helps make your code more readable.

What is the Walrus Operator?

The walrus operator (:=) lets you assign and return a value in the same expression. This means you can calculate a value, assign it to a variable, and use it immediately, all in one line. For example:

if (n := len(data)) > 10:
    print(f"List is too long ({n} elements, expected <= 10)")

Here, n gets the value of len(data), and we immediately check if n is greater than 10. This avoids the need for a separate assignment line.

Why Use the Walrus Operator?

  1. Reduced Lines of Code: Simplify your code by combining assignment and expression.

  2. Improved Readability: Keeps related logic together, making your code easier to understand.

  3. Performance: In some cases, avoids redundant calculations, improving performance.

Practical Examples of the Walrus Operator

Let’s explore some scenarios where the walrus operator can shine.

In Loops

The walrus operator is particularly handy in loops. It allows you to perform a calculation once, use it in the loop condition, and continue using the result within the loop body:

# Without walrus operator
line = file.readline().strip()
while line:
    line = file.readline().strip()

# With walrus operator
while (line := file.readline().strip()):

Here, line is assigned the value of file.readline().strip() and checked in the while loop condition. The loop continues until line is empty or None.

In Conditional Statements

The walrus operator can also make conditional statements more concise:

# Without walrus operator
match = pattern.search(data)
if match:
    print(f"Found match: {match.group(0)}")

# With walrus operator
if (match := pattern.search(data)) is not None:
    print(f"Found match: {match.group(0)}")

In this example, match is assigned the result of pattern.search(data), and we immediately check if match is not None. If a match is found, we print it.

In List Comprehensions

List comprehensions can also benefit from the walrus operator, making them more powerful and expressive:

# Without walrus operator
results = []
for x in data:
    y = f(x)
    if y > 0:

# With walrus operator
results = [y for x in data if (y := f(x)) > 0]

In this list comprehension, y is assigned the result of f(x) and then checked if it is greater than 0 before being included in the results list.

Controversy and Best Practices

Despite its benefits, the walrus operator has sparked debate among Python developers. Some find it a valuable addition, while others argue that it can make code harder to read, especially for those not familiar with this syntax. As with any feature, the key is to use it judiciously. Overuse or misuse can lead to code that’s difficult to understand and maintain.


The walrus operator (:=) is a valuable addition to Python 3.8, offering a way to write cleaner and more efficient code. It can enhance both the readability and performance of your code when used properly. Remember, the key to using the walrus operator effectively is to apply it in situations where it makes your code clearer and more concise.

Next time you find yourself writing extra lines to assign and check a value, consider if the walrus operator can simplify your code. Happy coding!