import time
def test1():
while True:
print('.....1......')
time.sleep(0.2)
yield
def test2():
while True:
print('......2......')
time.sleep(0.2)
yield
def main():
t1 = test1()
t2 = test2()
while True:
next(t1)
next(t2)
if __name__ == '__main__':
main()