How come an abstract base class in python can be instantiated?

Question

It is very surprising to me that I can instantiate an abstract class in python:

from abc import ABC class Duck(ABC): def __init__(self, name): self.name = name if __name__=="__main__": d = Duck("Bob") print(d.name)

The above code compiles just fine and prints out the expected result. Doesn't this sort of defeat the purpose of having an ABC?

If you have no abstract methods, what's the point of using an ABC? — wim
– wim, Commented Feb 2, 2022 at 7:44
Good point, but then it would be nice if the docs explicitly stated that the combination of ABC and abstractmethod is what makes a true abstract class in python. — user32882
– user32882, Commented Feb 2, 2022 at 7:48
It's explicitly stated in the PEP (search for "at least one method"). And it's sort-of stated in the docs too ("...cannot be instantiated unless all of its abstract methods and properties are overridden" - if there are no abstract methods, then it's actually true that all of them have been overridden) — wim
– wim, Commented Feb 2, 2022 at 9:18

robertspierre · Accepted Answer · 2024-12-18 07:30:50Z

If you have no abstract method, you will able to instantiate the class. If you have at least one, you will not.

Consider the following code:

from abc import ABC, abstractmethod class Duck(ABC): def __init__(self, name): self.name = name @abstractmethod def implement_me(self): ... if __name__=="__main__": d = Duck("Bob") print(d.name)

which returns:

TypeError: Can't instantiate abstract class Duck with abstract method implent_me

It is the combination of the ABC metaclass, and at least one abstractmethod that will lead to you not being able to instantiate a class. If you leave out one of the two, you will be able to do so.

@user32882 no, this answer is correct. The above code compiles just fine, but throws that runtime error.
Never mind. You're right, adding an abstractmethod means the code won't run...

Sonatus · Accepted Answer · 2025-11-12 22:37:21Z

I had the same problem! I guess we can just make __init__() abstract:

from abc import ABC, abstractmethod class Duck(ABC): @abstractmethod def __init__(self, name): self.name = name

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