Walrus Operator: Assign a Variable in an Expression

The walrus operator (:=) in Python 3.8+ allows you to assign a variable in an expression, making your code more readable and efficient. It’s useful in two main scenarios:

1. Giving a meaningful name to a complex expression for better readability.
2. Avoiding repeated computations by reusing a variable instead of recomputing the expression.

Let’s consider an example where we want to calculate the radius, area, and volume of a circle given its diameter and height:

from math import pi

diameter = 4
height = 2

Without the walrus operator, we might compute the radius and area multiple times:

circle = {
    "radius": diameter / 2, # computed twice
    "area": pi * (diameter / 2)**2, # computed twice
    "volume": pi * (diameter / 2)**2 * height,
}

2.0

To avoid repeated computations, we can assign the radius and area to variables before creating the dictionary:

radius = diameter / 2
area = pi * radius**2

circle = {
    "radius": radius,
    "area": area,
    "volume": area * height,
}

2.0

To make the code more concise, we can use the walrus operator to assign the radius and area to variables while creating the dictionary.

circle = {
    "radius": (radius := diameter / 2),
    "area": (area := pi * radius**2),
    "volume": area * height,
}

After executing the code with the walrus operator, we can access the assigned variables:

print(radius)
print(area)

2.0
12.566370614359172

By using the walrus operator, we can simplify our code, reduce repeated computations, and improve readability.