A short python script showing the lifecycle methods of a metaclass

meta.py

#!/usr/bin/env python3


class Meta(type):
    """
    Keeps track of classes derived from a base
    """

    @classmethod
    def __prepare__(cls, name, bases, **kwds):
        return super().__prepare__(name, bases, **kwds)

    def __new__(cls, name, bases, attributes, **kwds):
        print('about to create {!r}'.format(name))
        record = super().__new__(cls, name, bases, attributes, **kwds)
        print('created {!r}'.format(record))
        return record

    def __init__(self, name, bases, attributes, **kwds):
        super().__init__(name, bases, attributes, **kwds)
        print('decorating {}'.format(self))
        # self.alec_foo = name
        return

    def __call__(self, **kwds):
        return super().__call__(**kwds)


class Base(metaclass=Meta):
    """
    Base class for keeping track of sublcasses
    """

    alec_foo = 'Base'

    def __init__(self, **kwds):
        super().__init__(**kwds)
        print('Base.__init__: {}'.format(self.alec_foo))
        self.alec_foo = 'mine'
        print('Base.__init__: {}'.format(self.alec_foo))
        return


class Derived(Base):
    """
    A derived class
    """

b = Base()
d = Derived()


# end of file