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How to define an abstract class in python and enforce variables

So I'm trying to define an abstract base class with a couple of variables that I want to make mandatory for any class that "inherits" that 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 an 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??

Perhaps I am using the wrong terminology .. but basically, I want every developer to "implement" the above class to force these variables to be defined

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2 answers


Update : abc.abstractproperty

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


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