[New-bugs-announce] [issue35815] Able to instantiate a subclass with abstract methods from __init_subclass__ of the ABC

[Jazeps Basko]

New submission from Jazeps Basko <jazeps.basko at gmail.com>:

I am creating and registering singleton instances of subclasses of ABC in the ABC's __init_subclass__ and I just noticed that I am able to instantiate even the classes which have abstract methods.



import abc


class Base(abc.ABC):
    def __init_subclass__(cls, **kwargs):
        instance = cls()
        print(f"Created instance of {cls} easily: {instance}")


    @abc.abstractmethod
    def do_something(self):
        pass


class Derived(Base):
    pass


Actual Output:

Created instance of <class '__main__.Derived'> easily: <__main__.Derived object at 0x10a6dd6a0>

Expected Output:

TypeError: Can't instantiate abstract class Derived with abstract methods do_something

----------
messages: 334284
nosy: jbasko
priority: normal
severity: normal
status: open
title: Able to instantiate a subclass with abstract methods from __init_subclass__ of the ABC
type: behavior
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35815>
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