No error while instantiating abstract class, even though abstract method is not implemented

Question

I was trying out the below python code:

from abc import ABCMeta, abstractmethod

class Bar:

    __metaclass__ = ABCMeta

    @abstractmethod
    def foo(self):
        pass


class Bar2(Bar):
    def foo2(self):
        print("Foo2")


b = Bar()
b2 = Bar2()

I thought having @abstractmethod will ensure that my parent class will be abstract and the child class would also be abstract as it is not implementing the abstract method. But here, I get no error trying to instantiate both the classes.

Can anyone explain why?

I did got exception `b=Bar() TypeError: Can't instantiate abstract class Bar with abstract methods foo` — Tanveer Alam, Feb 24 '15 at 05:50
@TanveerAlam Even I am surprised...I dont get the error...is it because of version? I am using 3.4 — codingsplash, Feb 24 '15 at 05:52

score 7 · Accepted Answer · edited Feb 14 '17 at 00:40

7

You must set meta-class of Bar class to ABCMeta.

Python 2:

class Bar:
    __metaclass__ = ABCMeta

    @abstractmethod
    def foo(self):
        pass

Python 3:

class Bar(object, metaclass=ABCMeta):
    @abstractmethod
    def foo(self):
        pass

edited Feb 14 '17 at 00:40

nbro

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answered Feb 24 '15 at 05:43

M.javid

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Additionally, there must be at least one abstract method in order for the error to be raised, like in your examples. – Aleksandar Jovanovic Feb 05 '17 at 15:39

No error while instantiating abstract class, even though abstract method is not implemented

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