Control Flow

Assignment Expressions

The walrus operator assigns a value inside an expression.

An assignment expression can name a computed value while a condition tests it. Here empty strings are skipped because their length is zero.

Source

messages = ["hello", "", "python"]

for message in messages:
    if length := len(message):
        print(message, length)

Output

hello 5
python 6

The same idea works in loops that read state until a sentinel appears. The assignment and comparison stay together.

Source

queue = ["retry", "ok"]
while (status := queue.pop(0)) != "ok":
    print(status)
print(status)

Output

retry
ok

Notes

Run the complete example

hello 5
python 6
retry
ok

Execution time appears here after you run the example.