python metaclass應用

1.abs實現抽象類就是需要修改metaclass
2.django中的orm也是修改metaclass

3.通過mytype創建對象,實現繼承

class MyType(type):
    def __init__(self, *args, **kwargs):
        super(MyType, self).__init__(*args, **kwargs)

    def __call__(cls, *args, **kwargs):
        print('xxxx')
        return super(MyType, cls).__call__(*args, **kwargs)

# Base = MyType('Base', (object,), {})
# MyType('Base', (object,), {}) 是有MyType創建； metaclass=MyType
# 1. type可以創建類metaclass=type；MyType也可以創建類metaclass=MyType
# 2. Base = MyType('Base', (object,), {}) -->
# class Base(metaclass=MyType):
#     pass
# class Foo(Base):
#     pass

class Foo(MyType('Base', (object,), {})):
    pass
obj = Foo()

4.通過封裝函數來創建新的對象,更加方便

class MyType(type):
    def __init__(self, *args, **kwargs):
        super(MyType, self).__init__(*args, **kwargs)

    def __call__(cls, *args, **kwargs):
        return super(MyType, cls).__call__(*args, **kwargs)


def with_metaclass(base):
    return MyType('XX', (base,), {})


class Foo(with_metaclass(object)):
    pass