Parent method with extra arguments in Python

Question

Parent class has a property called 'deserialize' that is static and abstract with one argument. Each Child class implemented that method. Now I have a situation that Child class needs more than one argument. When I add options=None to Parent class, children classes complain that they have a different signature(warning). I have to add options=None to each class. That is a refactoring. I want to know if I can omit the warning and continue, or there is a better solution? Or do I have to refactor?

class Serializable:
    __metaclass__ = ABCMeta

    @staticmethod
    @abstractmethod
    def deserialize(json_obj, options=None):
        pass

class ChildWithNoExtraArguments(Serializable):

   # warning is here...
   @staticmethod        
   def deserialize(json_obj):
        # some implementation

class ChildWithExtraArgumnets(Serializable):

    @staticmethod
    def deserialize(json_obj, options):
        # some implementation, I need options

@Code-Apprentice because of the OOP conditions. I mean we need that be static. — Amir Shabani, Feb 14 '18 at 18:27
@Code-Apprentice I mean: [When to use static method](https://stackoverflow.com/a/2671529/4360116) — Amir Shabani, Feb 15 '18 at 05:32
@Code-Apprentice You asked why static method. It is clear. In my situation deserialize method is not associated to any instance. It doesn't need an instance to do it's behavior. It is class level method. — Amir Shabani, Feb 15 '18 at 05:37
If it was clear, I wouldn't have had to ask. I am trying to understand what you are doing so that I can help you find a solution. Thank you for finally answering my question directly and clearly. — Code-Apprentice, Feb 15 '18 at 05:39
No need to apologize. Just remember that clear and direct answers are often the most helpful on this site. I think Matt has answered your question better than I can, so I will leave off here. Good luck to you in your programming endeavors. — Code-Apprentice, Feb 15 '18 at 05:54

Matt Hardcastle · Accepted Answer · 2018-02-14T18:56:45.217

3

You need to decorate your child classes deserialize implementation with @staticmethod too. The exception you're seeing is because python is automatically adding self to each of the method calls. Decorating then with @staticmethod stops this behavior.

Additionally, you're second implementation needs to define options as a keyword argument. Keyword arguments have default values, for instance: options=None.

class Serializable:
    __metaclass__ = ABCMeta

    @staticmethod
    @abstractmethod
    def deserialize(json_obj, options=None):
        pass

class ChildWithNoExtraArguments(Serializable):

   # warning is here...        
    @staticmethod
    def deserialize(json_obj, options=None):
        # some implementation

class ChildWithExtraArgumnets(Serializable):

    @staticmethod
    def deserialize(json_obj, options=None):
        # some implementation, I need options

edited Feb 14 '18 at 18:56

answered Feb 14 '18 at 14:52

Matt Hardcastle

638
3
9

Sorry, I added @staticmethod to subclasses. I updated my question. – Amir Shabani Feb 14 '18 at 18:24
We're almost there. I updated my response to address your other issue. Hopefully that helps. – Matt Hardcastle Feb 14 '18 at 18:57
Thanks, I know that I can do this. I have to refactor all of my methods. So maybe this is the only solution. – Amir Shabani Feb 15 '18 at 05:30
1

you could use the `deserialize(json_obj, **kwargs)` to suck up options, and any other keyword arguments. The `**` is a bit of syntax that tells Python to put any remaining keyword arguments into a dictionary named kwargs. – Matt Hardcastle Feb 15 '18 at 18:34

Parent method with extra arguments in Python

1 Answers1