Writing a class which returns different instances depending on an external factor.

gistfile1.txt

#!/usr/bin/python3 -tt

import abc
import os


class Base(metaclass=abc.ABCMeta):
    @abc.abstractmethod
    def run(self):
        pass


class Other1(Base):
    def run(self):
        print('Other1')


class Other2(Base):
    def run(self):
        print('Other2')


class Test(Base):
    def __new__(cls, *args, **kwargs):
        if os.environ.get('TESTING', False):
            return Other1(*args, **kwargs)
        return Other2(*args, **kwargs)


Test().run()