How to use @abstractmethod to create an abstract interface that specifies the argument structure of its constructor?

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I understand why the code below throws and exception, and some ways avoid that exception, but I don't understand the intended way to use @abstractmethod in order to create an abstract interface.

My goal is to

  • create an abstract interface Foo that has a single argument constructor
  • and an adapter class FooAdapter that can be subclassed by classes intending to implement Foo.

The problem is that if I add in the appropriate calls to "super" in the constructor I will eventually call the abstractmethod and raise an exception.

  • Fix #1. Dont add super. works but seems wrong since it could drop info needed by other classes, if mixed with other classes
  • Fix #2. Dont add the signature for init in the interface. works, but seems wrong since the whole point of an interface is to DEFINE THE INTERFACE. and I would not be doing that, at least not for the constructor.

I feel like I am thinking about this wrong. What the pythonic way??


from abc import ABC, abstractmethod

class Foo(ABC):
    @abstractmethod
    def __init__(self, my_arg):
        raise NotImplementedError


class FooAdapter(Foo):
    def __init__(self, my_arg):
        super().__init__()

FROM THE ACCEPTED ANSWER BELOW

You don't need to use NotImplementedError at all, instead just use 'pass'. The @abstractmethod mechanism will throw an exception if a subclass does not implement the indicated method.

abstract-class interface inheritance oop python
1 Answers

From abc.abstarctmethod description:

Note: Unlike Java abstract methods, these abstract methods may have an implementation. This implementation can be called via the super() mechanism from the class that overrides it. This could be useful as an end-point for a super-call in a framework that uses cooperative multiple-inheritance.

Therefore you need just put stub doing nothing instead of raising NotImlementedError.

user_137826690
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