import time

print('按下回车开始计时，按下 Ctrl + C 停止计时。')

while True:

input("")

start = time.time()

print('计时开始')

try:

while True:

x=time.time()-start

ms=int(x%1*1000)

s=int(x%60)

m=int(x//60%60)

h=int(x//60//60)

print('{:0>2d}:{:0>2d}:{:0>2d}:{:0>3d}'.format(h,m,s,ms),end='\r')

time.sleep(0.001)

except KeyboardInterrupt:

break

print('{:0>2d}:{:0>2d}:{:0>2d}:{:0>3d}'.format(h,m,s,ms))

print('计时结束')