In Python, how to enforce an abstract method to be static on the base class?

Vote count:

1

This is the setup I want: A should be an abstract base class with a static & abstract method f(). B should inherit from A. Requirements: 1. You should not be able to instantiate A 2. You should not be able to instantiate B, unless it implements a static f()

Taking inspiration from this question, I've tried a couple of approaches. With these definitions:

class abstractstatic(staticmethod):
    __slots__ = ()
    def __init__(self, function):
        super(abstractstatic, self).__init__(function)
        function.__isabstractmethod__ = True
    __isabstractmethod__ = True

class A:
    __metaclass__ = abc.ABCMeta
    @abstractstatic
    def f():
        pass

class B(A):
    def f(self):
        print 'f'

class A2:
    __metaclass__ = abc.ABCMeta
    @staticmethod
    @abc.abstractmethod
    def f():
        pass

class B2(A2):
    def f(self):
        print 'f'

Here A2 and B2 are defined using usual Python conventions and A & B are defined using the way suggested in this answer. Following are some operations I tried and the results that were undesired.

With classes A/B:

>>> B().f()
f
#This should have thrown, since B doesn't implement a static f()

With classes A2/B2:

>>> A2()
<__main__.A2 object at 0x105beea90>
#This should have thrown since A2 should be a base class

>>> B2().f()
f
#This should have thrown, since B2 doesn't implement a static f()

Since neither of these approaches give me the output I want, how do I achieve what I want?

asked 1 min ago

GrowinMan

1,045

In Python, how to enforce an abstract method to be static on the base class?