在抽象 class 中编写 python 装饰器，并在继承的 class 中使用它

Question

TL;DR: I want to run some logic (eg update database) inside an abstract class. maybe there is another way to do it, that's what i could think of so far (using a decorator)

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I have the following abstract class:

class MyAbstractClass(metaclass=abc.ABCMeta):

    @abc.abstractmethod
    def my_abstract_method(self, request):
        pass

    @staticmethod
    def decorator_func(self, func):
        def run_func(param_one, param_two):
            print('INSIDE run_func', param_one, param_two)
            results = self.update_database(param_one, param_two)
            func(test_id, request)
            print('FINISHED run_func')

        return run_func

    def update_database(self, param_one, param_two):
        results = <DO SOME BACKEND CALCULATIONS>
        return results

I want to create a child class that inherit from this class, and use the decorator_func in order to do some database-updates in the abstract method my_abstract_method :

class ChildClass(MyAbstractClass):
    def __init__(self):
        super().__init__()

    @MyAbstractClass.decorator_func
    def my_abstract_method(self, request):
        get_data()

So i know that my_abstract_method will get updated data because the decorator made sure to run update_database before.

I tried a lot of combinations (eg removing the @staticmethod or trying to apply it with @classmethod) but it won't work. for the current code i get the error: run_func() takes 2 positional arguments but 3 were given

Any ideas about how can i easily run update_database before the my_abstract_method will run?

Answer 1

The static method gets one argument, the function being decorated. The function it returns is the one that needs a parameter to hold the implicit instance argument received by a method call.

@staticmethod
def decorator_func(func):
    def run_func(self, param_one, param_two):
        print('INSIDE run_func', param_one, param_two)
        results = self.update_database(param_one, param_two)
        func(self, test_id, request)
        print('FINISHED run_func')

    return run_func

Because func is a reference to a function , not a bound method, you need to pass self explicitly as the first argument.