python学习之hook钩子的原理和使用

什么是钩子

之前有转一篇关于回调函数的文章

钩子函数、注册函数、回调函数,他们的概念其实是一样的。

钩子函数,顾名思义,就是把我们自己实现的hook函数在某一时刻挂接到目标挂载点上。

1. hook函数,就是我们自己实现的函数,函数类型与挂载点匹配(返回值,参数列表)

2. 挂接,也就是hook或者叫注册(register),使得hook函数对目标可用

3. 目标挂载点,也就是挂我们hook函数的地方(我们想在这个目标点实现我们自己的功能)

先看一张图:

 

hook的概念在windows的消息响应机制里面体现的尤为明显。可能我们大家有写过windows桌面相关的程序(像MFC),里面有各种消息监听响应机制。比如,要监听鼠标左键是否按下这个事件,我们要去实现一个onLeftKeyDown()之类的方法,该方法可以称为钩子函数。同时,我们还要去注册钩子函数,MFC中是通过一组宏来实现的。这样当鼠标左键按下后,就能调到我们定义的方法了。

为什么需要钩子

大家思考一下上面这个例子,左键按下方法具体的逻辑是由框架自身去实现,还是由我们用户(调用者)去实现呢?显然应该由我们自己去实现。要提供通用的框架能力,框架自身去实现该方法功能,是没有意义的,所以框架给提供一个挂载的point,把具体逻辑的实现交给用户就好了,灵活可用。

钩子使用

hook是一个编程机制,与语言无关。这里给个python的简单例子,帮助大家理解:

import time

class LazyPerson(object):

def __init__(self, name):

self.name = name

self.watch_tv_func = None

self.have_dinner_func = None

def get_up(self):

print("%s get up at:%s" % (self.name, time.time()))

def go_to_sleep(self):

print("%s go to sleep at:%s" % (self.name, time.time()))

def register_tv_hook(self, watch_tv_func):

self.watch_tv_func = watch_tv_func

def register_dinner_hook(self, have_dinner_func):

self.have_dinner_func = have_dinner_func

def enjoy_a_lazy_day(self):

# get up

self.get_up()

time.sleep(3)

# watch tv

# check the watch_tv_func(hooked or unhooked)

# hooked

if self.watch_tv_func is not None:

self.watch_tv_func(self.name)

# unhooked

else:

print("no tv to watch")

time.sleep(3)

# have dinner

# check the have_dinner_func(hooked or unhooked)

# hooked

if self.have_dinner_func is not None:

self.have_dinner_func(self.name)

# unhooked

else:

print("nothing to eat at dinner")

time.sleep(3)

self.go_to_sleep()

def watch_daydayup(name):

print("%s : The program ---day day up--- is funny!!!" % name)

def watch_happyfamily(name):

print("%s : The program ---happy family--- is boring!!!" % name)

def eat_meat(name):

print("%s : The meat is nice!!!" % name)

def eat_hamburger(name):

print("%s : The hamburger is not so bad!!!" % name)

if __name__ == "__main__":

lazy_tom = LazyPerson("Tom")

lazy_jerry = LazyPerson("Jerry")

# register hook

lazy_tom.register_tv_hook(watch_daydayup)

lazy_tom.register_dinner_hook(eat_meat)

lazy_jerry.register_tv_hook(watch_happyfamily)

lazy_jerry.register_dinner_hook(eat_hamburger)

# enjoy a day

lazy_tom.enjoy_a_lazy_day()

lazy_jerry.enjoy_a_lazy_day()

代码运行结果:

Tom get up at:1509246940.32

Tom : The program ---day day up--- is funny!!!

Tom : The meat is nice!!!

Tom go to sleep at:1509246949.34

Jerry get up at:1509246949.34

Jerry : The program ---happy family--- is boring!!!

Jerry : The hamburger is not so bad!!!

Jerry go to sleep at:1509246958.37

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