Python Walrus Operator

What is the Walrus Operator?

Introduced in Python 3.8, the walrus operator := creates what is called an assignment expression: it assigns a value to a name and also produces that value as a result, all within a single expression, unlike a normal = assignment statement.

if (n := 10) > 5:
    print(f"{n} is greater than 5")

Using it in a while Loop

A common use case is reading input or data until some condition is met. Without the walrus operator, you often need to assign a value before the loop and again inside it. With :=, you can do both in one line.

# Without walrus
line = input("Enter text: ")
while line != "":
    print("Got:", line)
    line = input("Enter text: ")

# With walrus
while (line := input("Enter text: ")) != "":
    print("Got:", line)

Using it in Comprehensions

The walrus operator also helps inside list comprehensions when you need to use the result of an expensive computation more than once, without repeating the computation.

data = [1, 4, 9, 16, 25, 36]

# Only keep square roots that are whole numbers, without calling sqrt twice
import math
results = [root for n in data if (root := math.sqrt(n)).is_integer()]
print(results)

Readability Considerations

The walrus operator is a convenience, not a requirement — it can make code shorter, but overusing it can also make expressions harder to read. Use it when it removes clear duplication, and skip it when a plain assignment statement is easier to follow.