how to define an abstract class in python and force implement variables

Question

So, I am trying to define an abstract base class with couple of variables which I want to to make it mandatory to have for any class which "inherits" this base class.. So, something like:

class AbstractBaseClass(object):
   foo = NotImplemented
   bar = NotImplemented

Now,

class ConcreteClass(AbstractBaseClass):
    # here I want the developer to force create the class variables foo and bar:
    def __init__(self...):
        self.foo = 'foo'
        self.bar = 'bar'

This should throw error:

class ConcreteClass(AbstractBaseClass):
    # here I want the developer to force create the class variables foo and bar:
    def __init__(self...):
        self.foo = 'foo'
        #error because bar is missing??

I maybe using the wrong terminology.. but basically, I want every developer who is "implementing" the above class to force to define these variables??

Answer 1

Update : abc.abstractproperty has been deprecated in Python 3.3. Use property with abc.abstractmethod instead as shown here .

import abc

class AbstractBaseClass(object):

    __metaclass__ = abc.ABCMeta

    @abc.abstractproperty
    def foo(self):
        pass

    @abc.abstractproperty
    def bar(self):
        pass

class ConcreteClass(AbstractBaseClass):

    def __init__(self, foo, bar):
        self._foo = foo
        self._bar = bar

    @property
    def foo(self):
        return self._foo

    @foo.setter
    def foo(self, value):
        self._foo = value

    @property
    def bar(self):
        return self._bar

    @bar.setter
    def bar(self, value):
        self._bar = value

Answer 2

class AbstractBaseClass(object):
    def __init__(self):
        assert hasattr(self, 'foo')
        assert hasattr(self, 'bar')