Python object creation - metaclasses

meta.py

class Meta(type):
     @classmethod
     def __prepare__(mcs, name, bases, **kwargs):
         print('  Meta.__prepare__(mcs=%s, name=%r, bases=%s, **%s)\n' % (
             mcs, name, bases, kwargs
         ))
         return {}

     def __new__(mcs, name, bases, attrs, **kwargs):
         print('  Meta.__new__(mcs=%s, name=%r, bases=%s, attrs=[%s], **%s)\n' % (
             mcs, name, bases, ', '.join(attrs), kwargs
         ))
         return super().__new__(mcs, name, bases, attrs) # equals to type.__new__(...)

     def __init__(cls, name, bases, attrs, **kwargs):
         print('  Meta.__init__(cls=%s, name=%r, bases=%s, attrs=[%s], **%s)\n' % (
             cls, name, bases, ', '.join(attrs), kwargs
         ))
         return super().__init__(name, bases, attrs)

     def __call__(cls, *args, **kwargs):
         print('  Meta.__call__(cls=%s, args=%s, kwargs=%s)\n' % (
             cls, args, kwargs
         ))
         return super().__call__(*args, **kwargs)
class Class(metaclass=Meta, extra=1):
     def __new__(cls, myarg):
         print('  Class.__new__(cls=%s, myarg=%s)\n' % (
             cls, myarg
         ))
         return super().__new__(cls)

     def __init__(self, myarg):
         print('  Class.__init__(self=%s, myarg=%s)\n' % (
             self, myarg
         ))
         self.myarg = myarg
         return super().__init__()

     def __str__(self):
         return '<instance of Class; myargs=%s>\n' % (
             getattr(self, 'myarg', 'MISSING'),
         )

Class(1)

# >>> result

#   Meta.__prepare__(mcs=<class '__main__.Meta'>, name='Class', bases=(), **{'extra': 1})

#   Meta.__new__(mcs=<class '__main__.Meta'>, name='Class', bases=(), attrs=[__str__, __module__, __init__, __qualname__, __new__], **{'extra': 1})

#   Meta.__init__(cls=<class '__main__.Class'>, name='Class', bases=(), attrs=[__str__, __module__, __init__, __qualname__, __new__], **{'extra': 1})

#   Meta.__call__(cls=<class '__main__.Class'>, args=(1,), kwargs={})

#   Class.__new__(cls=<class '__main__.Class'>, myarg=1)

#   Class.__init__(self=<instance of Class; myargs=MISSING>, myarg=1)