break out nested loops

#!/usr/bin/env python3
import contextlib

@contextlib.contextmanager
def Label(name):
    class _Label(Exception):
        pass
    try:
        yield _Label
    except _Label:
        print("loop break:", name)

with Label("label1") as label1:
    for x in range(5):
        print("L1", x)
        with Label("label2") as label2:
            for y in range(10, 50, 10):
                print("L2", y)
                for z in range(100, 500, 100):
                    print("L3", z)
                    if x > 1:
                        raise label1()
                    if y > 10:
                        raise label2()
                    if z > 200:
                        print("loop break: L3")
                        break