w = h = d = 10  # for testing
for x in range(0, w):
    for y in range(0, h):
        for z in range(0, d):
            print x, y, z
            stop = raw_input("Stop? y/n")
            # alas this will only break out of the z loop
            if stop == "y":
                break

def nested_loop():
    """use of return to exit a nested loop"""
    w = h = d = 10  # for testing
    for x in range(0, w):
        for y in range(0, h):
            for z in range(0, d):
                print x, y, z
                stop = raw_input("Stop? y/n")
                if stop == "y":
                    return
 
nested_loop()

# use of try/except to exit a nested loop
w = h = d = 10  # for testing
try:
    for x in range(0, w):
        for y in range(0, h):
            for z in range(0, d):
                print x, y, z
                if raw_input("Stop? y/n") == "y":
                    raise StopIteration()
except StopIteration:
    pass