python线程问题

代码:

from threading import Thread, Event
import time


def countdown(n, start_env):
    print("countdown starting!")
    start_env.set()
    while n > 0:
        print("T-minus", n)
        n -= 1
        time.sleep(2)


start_env = Event()


print('Launching Thread-countdown')
t = Thread(target=countdown, args=(10, start_env))
t.start()


start_env.wait()
print("countdown Running..............")
t.join()

输出结果:

Launching Thread-countdown
countdown starting!
T-minus 10
countdown Running..............
T-minus 9
T-minus 8
T-minus 7
T-minus 6
T-minus 5
T-minus 4
T-minus 3
T-minus 2
T-minus 1

我想问:为什么countdown Running 只在T-minus 10后输出一次?

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