How to declare a variable to be implemented in the subclass in python?

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Update

Actually, I have tested all the answers, but a feature I want still can't be achieved. Using @property force the subclass to directly declare the property but not something like self.property = xxx in one function. How could I also achieve this?

I mean, if the subclass __get__ the property before __set__, then raise NotImplementedError.

How to declare a variable in the super class which should be implemented in the subclass?

In other word, I want to declare a virtual variable in super class.

class A:

    def a(self):               # perfect!
        raise NotImplementedError("...") 

    b = raise NotImplementedError("...")      #how to declare a variable similar with the function above?

score 1 · Accepted Answer · answered May 08 '17 at 10:33

Since Python doesn't really have something called virtual objects, you can mimic in case of methods by explicitly raising exception but in the case of variables, you can either override __init__ or use properties instead of variables.

class A(object):

    def __init__(self, *args, **kwargs):
        if not hasattr(self, 'b'):
            raise NotImplementedError("...")

class B(A):
    b = 3

score 0 · Answer 2 · edited May 23 '17 at 11:47

0

You can use the property decorator. For more information, please check this thread where you can get a detailed answer.

edited May 23 '17 at 11:47

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answered May 08 '17 at 10:34

blasrodri

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How to declare a variable to be implemented in the subclass in python?

Update

2 Answers2