Example of a factory superclass, which constructor returns a new instance of the correct subclass for a given parameter.

factory_superclass.py

class Animal(object):
    
    def __new__(cls, common_name, *args, **kwargs):
        for subclass in cls.__subclasses__():
            if subclass.common_name == common_name:
                return object.__new__(subclass, *args, **kwargs)
        
        raise ValueError('No animal species matched for common name "{}"'.format(common_name))


class CanisLupusFamiliaris(Animal):
    common_name = 'dog'

class FelisCatus(Animal):
    common_name = 'cat'

# Get a dog instance: OK
dog = Animal('dog')
assert type(dog) == CanisLupusFamiliaris

# Get a cat instance: OK
cat = Animal('cat')
assert type(cat) == FelisCatus

# Get spider instance: error (no animal species matched)
Animal('spider')