Creating abstract method

Very popular method to declare an abstract method in Python class is to use NotImplentedError exception:

class SomeWorker:
    def do_work(self):
        raise NotImplementedError

This method even has IDE support (I use PyCharm, so at least it supports it).

The only downside of this approach is that you get the error only after method call.

>>> w = MyWorker()
# it's ok
>>> w.do_work()

NotImplementedError

It would be much better to know about the problem right after class instantiation.

Python's abstract base classes are here to help

from abc import ABCMeta, abstractmethod

class SomeWorker(metaclass=ABCMeta):
    @abstractmethod
    def do_work(self):
        pass

For now if you subclass SomeWorker and doesn't override do_work - you will get an error right upon class instantiation

>>> w = MyWorker()
TypeError: Can't instantiate abstract class MyWorker with abstract methods do_work