python使用装饰器实现面向切面编程

一,装饰器的概念与使用

文章见https://www.jb51.net/article/153214.htm，本文不做过多赘述

二，装饰器实现面向切面编程的具体方法

众所周知，装饰器是python的语法糖，对于简化代码书写，提高代码复用具有很大意义，装饰器常用于打印日志，计时器，登录检查，其中django的login_required便是对页面访问进行约束，只有登陆才能访问页面，装饰器的作用包括但不仅限于此。

举个例子：

当前楼主的需求是：

假设django视图中存在耗时操作，但是遇到耗时操作，客户端便存在等待时间，这极大的影响了客户体验，俗话说用户就是上帝，我们需要制造一些假数据返回前台，告诉前台，后台数据在取数据这块由于不要可抗力造成卡顿延误。

菜鸟级解决方案：

对于每一个视图，增加超时时间，超时即返回默认空json字符串给前台

import json
import time
import signal
from django.http import HttpResponse
 
 
def view1():
    try:
        signal.signal(signal.SIGALRM, myHandler)
        signal.alarm(1)  # 设置超时时间一秒
        response = urllib2.urlopen("某一耗时网站A")
        result_str = json.loads(response.read())
        signal.alarm(0)
        return HttpResponse(result_str, content_type="application/json")
    except:
        return HttpResponse({}, content_type="application/json")
 
 
def view2():
    try:
        signal.signal(signal.SIGALRM, myHandler)
        signal.alarm(1)  # 设置超时时间一秒
        response = urllib2.urlopen("某一耗时网站B")
        result_str = json.loads(response.read())
        signal.alarm(0)
        return HttpResponse(result_str, content_type="application/json")
    except:
        return HttpResponse({}, content_type="application/json")
 
 
def view3():
    try:
        signal.signal(signal.SIGALRM, myHandler)
        signal.alarm(1)  # 设置超时时间一秒
        response = urllib2.urlopen("某一耗时网站C")
        result_str = json.loads(response.read())
        signal.alarm(0)
        return HttpResponse(result_str, content_type="application/json")
    except:
        return HttpResponse({}, content_type="application/json")
    
    
    
    
def view4():
    try:
        signal.signal(signal.SIGALRM, myHandler)
        signal.alarm(1)  # 设置超时时间一秒
        response = urllib2.urlopen("某一耗时网站D")
        result_str = json.loads(response.read())
        signal.alarm(0)
        return HttpResponse(result_str, content_type="application/json")
    except:
        return HttpResponse({}, content_type="application/json")

普通人解决方案，显然利用第二种方案，使用装饰器后不仅将代码模块化，而且更能清晰明了的表达代码作用

def TimeOut(func):
        def function(*args, **kwargs):
            try:
                signal.signal(signal.SIGALRM, myHandler)
                signal.alarm(1)
                stime = time.time()
                print("程序开始运行")
                func(*args, **kwargs)
                print("程序结束运行")
                print(time.time() - stime)
                signal.alarm(0)
            except:
                return HttpResponse({}, content_type="application/json")
        return function
 
 
@TimeOut
def view1():
    response = urllib2.urlopen("某一耗时网站A")
    result_str = json.loads(response.read())
    signal.alarm(0)
    return HttpResponse(result_str, content_type="application/json")
 
 
@TimeOut
def view2():
    response = urllib2.urlopen("某一耗时网站B")
    result_str = json.loads(response.read())
    return HttpResponse(result_str, content_type="application/json")
 
 
@TimeOut
def view3():
    response = urllib2.urlopen("某一耗时网站C")
    result_str = json.loads(response.read())
    return HttpResponse(result_str, content_type="application/json")
 
 
@TimeOut
def view4():
    response = urllib2.urlopen("某一耗时网站D")
    result_str = json.loads(response.read())
    return HttpResponse(result_str, content_type="application/json")

大神解决方案：对于每个视图函数定制化的返回需要的结果

def TimeOut(view):
    def wrap(func):
        def function(*args, **kwargs):
            try:
                signal.signal(signal.SIGALRM, myHandler)
                signal.alarm(1)
                stime = time.time()
                print("程序开始运行")
                func(*args, **kwargs)
                print("程序结束运行")
                print(time.time() - stime)
                signal.alarm(0)
            except:
                if view == "view1":
                    dict = "view1需要返回的结果"
                if view == "view2":
                    dict = "view2需要返回的结果"
                if view == "view3":
                    dict = "view3需要返回的结果"
                if view == "view4":
                    dict = "view4需要返回的结果"
                return HttpResponse(dict, content_type="application/json")
 
        return function
 
    return wrap
 
 
@TimeOut("view1")
def view1():
    response = urllib2.urlopen("某一耗时网站A")
    result_str = json.loads(response.read())
    signal.alarm(0)
    return HttpResponse(result_str, content_type="application/json")
 
 
@TimeOut("view2")
def view2():
    response = urllib2.urlopen("某一耗时网站B")
    result_str = json.loads(response.read())
    return HttpResponse(result_str, content_type="application/json")
 
 
@TimeOut("view3")
def view3():
    response = urllib2.urlopen("某一耗时网站C")
    result_str = json.loads(response.read())
    return HttpResponse(result_str, content_type="application/json")
 
 
@TimeOut("view4")
def view4():
    response = urllib2.urlopen("某一耗时网站D")
    result_str = json.loads(response.read())
    return HttpResponse(result_str, content_type="application/json")