python关于装饰器使用的的问题，如何解决？

Question

想用装饰器给这个函数计算运行时间，为什么一直不对啊,刚学，下面的错误也看不懂,谢谢各位

from time import *
def time_master(func):
    def time_(*args,**kwargs):
        print("开始调用程序")
        start=time()
        func(*args,**kwargs)
        stop=time()
        print("结束调用,共用时{:.5f}".format(stop-start))
    return time_

@time_master
def rabbit(m):
    if m<4:
        return m
    else:
        return rabbit(m-3)+rabbit(m-1)

print(rabbit(5))


错误显示
开始调用程序
开始调用程序
结束调用,共用时0.00000
开始调用程序
开始调用程序
结束调用,共用时0.00000
开始调用程序
结束调用,共用时0.00000
Traceback (most recent call last):
  File "C:\Users\13113\Desktop\递归.py", line 40, in <module>
    print(rabbit(5))
          ^^^^^^^^^
  File "C:\Users\13113\Desktop\递归.py", line 29, in time_
    func(*args,**kwargs)
  File "C:\Users\13113\Desktop\递归.py", line 38, in rabbit
    return rabbit(m-3)+rabbit(m-1)
                       ^^^^^^^^^^^
  File "C:\Users\13113\Desktop\递归.py", line 29, in time_
    func(*args,**kwargs)
  File "C:\Users\13113\Desktop\递归.py", line 38, in rabbit
    return rabbit(m-3)+rabbit(m-1)
           ~~~~~~~~~~~^~~~~~~~~~~~
TypeError: unsupported operand type(s) for +: 'NoneType' and 'NoneType'

进程已结束,退出代码1

Answer 1

代码修改如下, 增加 return,返回函数的执行结果

import time
from time import *


def time_master(func):
    def time_(*args, **kwargs):
        print("开始调用程序")
        start = time()
        res = func(*args, **kwargs)
        stop = time()
        print("结束调用,共用时{:.10f}".format(stop - start))
        return res

    return time_


@time_master
def rabbit(m):
    sleep(0.01)
    if m < 4:
        return m
    else:
        return rabbit(m - 3) + rabbit(m - 1)


print(rabbit(5))