CODEWITHSUNDEEP
pythonpython-2.7inheritanceabstract-class
swang
swang

Reputation: 5249

Should a python abstract base class inherit from object

The standard document about abc, and other tutorials I read all use examples that defines a abstract base class without inheriting from object. 

class Foo(object):
    def __getitem__(self, index):
        ...
    def __len__(self):
        ...
    def get_iterator(self):
        return iter(self)

class MyIterable:
    __metaclass__ = ABCMeta

    @abstractmethod
    def __iter__(self):
        while False:
            yield None

In the past I always let my class inherit object to have new-style class. Should I do the same with ABC?

Upvotes: 3

Views: 655

Answers (1)

Billy
Billy

Reputation: 5609

Declaring the metaclass of MyIterable to be ABCMeta ensures that instances of MyIterable (or more appropriately, subclasses of MyIterable since it is an Abstract Base Class) will be the "new" style. If you were to create an instance of a subclass of MyIterable as seen below, it would behave as a new style class.

class SubIterable(MyIterable):
    def __iter__(self):
        # your implementation here
        ...

>>> type(SubIterable())
<type '__main__'.MyIterable>

If MyIterable were indeed an "old" style class, type(SubIterable()) would return <type 'instance'>

Upvotes: 3

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