python - 在子类方法中向函数添加钩子(Hook)

Question

给定以下简化代码:

from abc import ABC, abstractmethod

class Parent(ABC):
    def __init__(self,*args,**kwargs):
        self.parent_name = 'SuperClass'
    
    # global hook to run before each subclass run()
    def global_pre_run_hook(self):
        pass
    
    @abstractmethod
    def run(self, *args, **kwargs):
        raise NotImplementedError()

        
        
class Child(Parent):
    def __init__(self,*args,**kwargs):
        super().__init__(*args,**kwargs)
        self.name = 'ChildClass'
    
    def run(self):
        print(f'my parent name is {self.parent_name}')
        print(f'my name is {self.name}')
        
        return 22
        
obj = Child()
result = obj.run()

有没有办法增加功能，让直接调用子类的run()方法时，先触发父类的hook函数？假设有一个父类和许多子类 - 我是否需要在每个 run() 定义的开头手动添加一个 call global hook()对于子类化 Parent() 的每个类？是否有 Pythonic 方法来完成此操作？

Answer 1

可能有一种方法可以使用合适的装饰器来做到这一点，但目前我认为你可能想出的最干净的解决方案是创建你自己的“装饰器”并在 Parent.__init__()，只要子类调用父类__init__()，它就会生效:

from abc import ABC, abstractmethod

def create_hook(func, hook):
    def wrapper(*args, **kwargs):
        hook()
        return func(*args, **kwargs)
    return wrapper

class Parent(ABC):
    def __init__(self, *args, **kwargs):
        self.parent_name = 'SuperClass'
        self.run = create_hook(self.run, self.global_pre_run_hook)

    # global hook to run before each subclass run()
    def global_pre_run_hook(self):
        print("Hooked")

    @abstractmethod
    def run(self, *args, **kwargs):
        raise NotImplementedError()

class Child(Parent):
    def __init__(self,*args,**kwargs):
        super().__init__(*args,**kwargs)
        self.name = 'ChildClass'

    def run(self):
        print(f'my parent name is {self.parent_name}')
        print(f'my name is {self.name}')
        return 22

obj = Child()
result = obj.run()
# this prints:
#   Hooked
#   my parent name is SuperClass
#   my name is ChildClass