方法一：

import time


class NumberList(object):
    def __enter__(self):
        self.start = time.time()
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.end = time.time()
        print("函数执行 %d 毫秒" % (self.end - self.start))

    def func(self, number):
        li = [1, 2, 4]
        if number < 4:
            return li[number - 1]
        else:
            if number > 3:
                return (self.func(number - 1)
                        + self.func(number - 2)
                        + self.func(number - 3))


with NumberList() as n:
    print(n.func(1000))

方法二：

import time
import contextlib


@contextlib.contextmanager
def timing():
    start = time.time()
    yield None
    end = time.time()
    print("函数执行时间是%d毫秒" % (end - start))


def func(number):
    li = [1, 2, 4]
    if number < 4:
        return li[number - 1]
    else:
        if number > 3:
            return func(number - 1) + func(number - 2) + func(number - 3)


with timing():
    print(func(30))