python 的钩子函数

一、什么是钩子函数

hook函数就是在一定条件下才会执行的函数，将自己实现的函数挂载到挂载点上

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

二、使用场景

一般在流程性的代码中会使用hook函数，挂载点可能会执行我们实现的函数，也可能不执行，当满足一定条件才会执行的情况下

import time

class LazyPerson(object):
    def __init__(self, name):
        self.name = name
        self.watch_tv_func = None # 目标挂载点
        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): # 挂接
        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):
        self.get_up()
        time.sleep(2)
        # 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)
        else: # unhooked
            print("no tv to watch")

        time.sleep(2)
        # 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)
        else: # unhooked
            print("nothing to eat at dinner")

        time.sleep(2)
        self.go_to_sleep()

def watch_daydayup(name): # hook函数
    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)

def test():
    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()

test()

钩子函数的实现就是通过一定的关系，将两个函数产生关联，例如上面的例子，register_tv_hook函数和watch_day_day_up通过self.watch_tv_func产生关联，如果要执行watch_tv_func函数，需要先进行注册（register_tv_hook），然后判断注册时传入的self.watch_tv_func是否为空，如果为空则表示注册未成功，则不执行我们自己写的函数watch_tv_func，如果不为空，则表示注册成功，则执行函数watch_day_day_up，大大扩展了类的可执行方法

参考文档：https://www.cnblogs.com/zhang-ye/p/16289417.html 、https://blog.csdn.net/RayMand168/article/details/128560646