小练习2

1#测试函数执行时间的装饰器示例
import time
def timing_func(fn):
    def wrapper():
        start=time.time()
        fn()   #执行传入的fn参数
        stop=time.time()
        return (stop-start)
    return wrapper
@timing_func
def test_list_append():
    lst=[]
    for i in range(0,100000):
        lst.append(i)  
@timing_func
def test_list_compre():
    [i for i in range(0,100000)]  #列表生成式
a=test_list_append()
c=test_list_compre()
print("test list append time:",a)
print("test list comprehension time:",c)
print("append/compre:",round(a/c,3))

test list append time: 0.0219423770904541
test list comprehension time: 0.007980823516845703
append/compre: 2.749

2.统计异常出现次数和时间的装饰器
写一个装饰器，统计某个异常重复出现指定次数时，经历的时长。

import time
import math


def excepter(f):
    i = 0
    t1 = time.time()
    def wrapper(): 
        try:
            f()
        except Exception as e:
            nonlocal i
            i += 1
            print(f'{e.args[0]}: {i}')
            t2 = time.time()
            if i == n:
                print(f'spending time:{round(t2-t1,2)}')
    return wrapper

3.定制递减迭代器

#编写一个迭代器，通过循环语句，实现对某个正整数的依次递减1，直到0.
class Descend(Iterator):
    def __init__(self,N):
        self.N=N
        self.a=0
    def __iter__(self):
        return self 
    def __next__(self):
        while self.a<self.N:
            self.N-=1
            return self.N
        raise StopIteration
    
descend_iter=Descend(10)
print(list(descend_iter))
[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]