metaclass.py

class Metaclass(type):

    def __new__(metacls, name, bases, namespace, **kwargs):
        cls = type.__new__(metacls, name, bases, namespace)
        print('>>> Metaclass.__new__(metacls={}, name={}, bases={}, namespace={}, **kwargs={})'.format(
            metacls, name, bases, namespace, kwargs, cls
        ))
        print(cls)
        return cls

    def __init__(cls, name, bases, namespace, **kwargs):
        print('>>> Metaclass.__init__(cls={}, name={}, bases={}, namespace={}, **kwargs={})'.format(
            cls, name, bases, namespace, kwargs
        ))
        super().__init__(name, bases, namespace)

    def __call__(cls, *args, **kwargs):
        instance = super().__call__(*args, **kwargs)
        print('>>> Metaclass.__call__(cls={}, *args={}, **kwargs={}'.format(
            cls, args, kwargs
        ))
        print(instance)
        return instance

    @classmethod
    def __prepare__(metacls, name, bases, **kwargs):
        print('>>> Metaclall.__prepare__(metacls={}, name={}, bases={}, **kwargs={})'.format(
            metacls, name, bases, kwargs
        ))
        print('{}')
        return dict()


class Object(metaclass=Metaclass, metakw='metakw'):

    def __new__(cls, *args, **kwargs):
        res = super().__new__(cls)
        print('>>> Object.__new__(cls=cls, *args={}, **kwargs={})'.format(
            cls, args, kwargs
        ))
        print(res)
        return res

    def __init__(self, *args, **kwargs):
        print('>>> Object.__init__(self={}, *args={}, **kwargs={})'.format(
            self, args, kwargs
        ))



>>> Metaclall.__prepare__(metacls=<class '__main__.Metaclass'>, name=Object, bases=(), **kwargs={'metakw': 'metakw'})
{}
>>> Metaclass.__new__(metacls=<class '__main__.Metaclass'>, name=Object, bases=(), namespace={'__new__': <function Object.__new__ at 0x7fd0c3159400>, '__qualname__': 'Object', '__init__': <function Object.__init__ at 0x7fd0c3159488>, '__module__': '__main__'}, **kwargs={'metakw': 'metakw'})
<class '__main__.Object'>
>>> Metaclass.__init__(cls=<class '__main__.Object'>, name=Object, bases=(), namespace={'__new__': <function Object.__new__ at 0x7fd0c3159400>, '__qualname__': 'Object', '__init__': <function Object.__init__ at 0x7fd0c3159488>, '__module__': '__main__'}, **kwargs={'metakw': 'metakw'})


class Descendant(Object, newmetakw='newmetakw'):

    def __new__(cls, *args, **kwargs):
        res = super().__new__(cls)
        print('>>> Descendant.__new__(cls=cls, *args={}, **kwargs={})'.format(
            cls, args, kwargs
        ))
        print(res)
        return res

    def __init__(self, *args, **kwargs):
        print('>>> Descendant.__init__(self={}, *args={}, **kwargs={})'.format(
            self, args, kwargs
        ))
        super().__init__(*args, **kwargs)

>>> Metaclall.__prepare__(metacls=<class '__main__.Metaclass'>, name=Descendant, bases=(<class '__main__.Object'>,), **kwargs={'newmetakw': 'newmetakw'})
{}
>>> Metaclass.__new__(metacls=<class '__main__.Metaclass'>, name=Descendant, bases=(<class '__main__.Object'>,), namespace={'__new__': <function Descendant.__new__ at 0x7fd0c3159510>, '__qualname__': 'Descendant', '__init__': <function Descendant.__init__ at 0x7fd0c3159598>, '__module__': '__main__'}, **kwargs={'newmetakw': 'newmetakw'})
<class '__main__.Descendant'>
>>> Metaclass.__init__(cls=<class '__main__.Descendant'>, name=Descendant, bases=(<class '__main__.Object'>,), namespace={'__new__': <function Descendant.__new__ at 0x7fd0c3159510>, '__qualname__': 'Descendant', '__init__': <function Descendant.__init__ at 0x7fd0c3159598>, '__module__': '__main__'}, **kwargs={'newmetakw': 'newmetakw'})

# Run time
>>> Object("arg", kwarg="kwargs")
>>> Object.__new__(cls=cls, *args=<class '__main__.Object'>, **kwargs=('arg',))
<__main__.Object object at 0x7fd0c31637f0>
>>> Object.__init__(self=<__main__.Object object at 0x7fd0c31637f0>, *args=('arg',), **kwargs={'kwarg': 'kwarg'})
>>> Metaclass.__call__(cls=<class '__main__.Object'>, *args=('arg',), **kwargs={'kwarg': 'kwarg'})
<__main__.Object object at 0x7fd0c31637f0>
<__main__.Object object at 0x7fd0c31637f0>

>>> Descendant("iarg", ikwarg="ikwargs")
>>> Object.__new__(cls=cls, *args=<class '__main__.Descendant'>, **kwargs=())
    <__main__.Descendant object at 0x7fd0c31638d0>
>>> Descendant.__new__(cls=cls, *args=<class '__main__.Descendant'>, **kwargs=('iarg',))
        <__main__.Descendant object at 0x7fd0c31638d0>
>>> Descendant.__init__(self=<__main__.Descendant object at 0x7fd0c31638d0>, *args=('iarg',), **kwargs={'ikwarg': 'ikwarg'})
>>> Object.__init__(self=<__main__.Descendant object at 0x7fd0c31638d0>, *args=('iarg',), **kwargs={'ikwarg': 'ikwarg'})
>>> Metaclass.__call__(cls=<class '__main__.Descendant'>, *args=('iarg',), **kwargs={'ikwarg': 'ikwarg'})
    <__main__.Descendant object at 0x7fd0c31638d0>
<__main__.Descendant object at 0x7fd0c31638d0>