Walrus Operator (:=) for Assignment Expressions

Patterns like compute a value, check it, then use it require either duplicating the computation or introducing an extra variable outside the conditional.

Use the walrus operator (:=) to assign and test in a single expression.

import re

# Without walrus: separate variable
result = re.search(r'\d+', text)
if result:
    print(result.group())

# With walrus: assign and check in one expression
if m := re.search(r'\d+', text):
    print(m.group())

# Useful in while loops
while chunk := file.read(8192):
    process(chunk)

# Filtering with list comprehension
results = [
    clean
    for raw in data
    if (clean := transform(raw)) is not None
]

The walrus operator assigns the result of an expression to a name and evaluates to that value. It reduces redundant computation and makes the compute-check-use pattern concise.