作为使用“条件”对象在python中练习线程间通信的一部分，我编写了以下代码

from threading import *
import time
c=Condition()

def sum():
    time.sleep(2)#if i comment this line then pgm waits,only sum() fun print stmt is executed
    c.acquire()
    print('here after this stms notify is called')
    c.notify()
    c.release()

def display():
    c.acquire()
    c.wait()
    print('display print is executing after notify')
    c.notify()
    c.release()

def show():
    c.acquire()
    c.wait()
    print('show print is executing after notify')
    c.release()

t2=Thread(target=display)
t3=Thread(target=show)
t1=Thread(target=sum)
t1.start()
t2.start()
t3.start()

pgm工作正常，但是如果我在time.sleep(2)函数中注释sum()，则仅执行sum（）函数的print stmt，然​​后等待。请告诉我为什么会发生这种情况，为什么这行time.sleep(2)会真正改变这种情况