Python简单的ProcessPoolExecutor示例不会工作

Question

我在Python 3中尝试多线程，但我无法弄清楚为什么我的例子不会起作用。它应该只打印数字，然后确认再次打印数字。 但它遇到了很多错误。

from concurrent import futures

def print_me(num):
    print('Zahl: ' + str(num))
    return num


def say_bye(job):
    num = job.result()
    print(str(num) + ' is out!')


def test_multi():
    num_list = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
    with futures.ProcessPoolExecutor(max_workers=4) as executor:
        for num in num_list:
            job = executor.submit(print_me, num)
            job.add_done_callback(say_bye(job))

test_multi()

理论上，而不是：

for num in num_list:
    job = executor.submit(print_me, num)
    job.add_done_callback(say_bye(job))`

我可以用这个，或者？

executor.map(print_me, num_list)

Answer 1

要使代码运行，我只需要添加：

if __name__ == "__main__":
    test_multi()