python中元类用法实例

class X:
...     a = 1
...
X = type('X', (object,), dict(a=1))

class OrderedClass(type):
     #该方法返回值就是__new__的namespace参数，如果没有该方法namespace的值就是dict()
     @classmethod
     def __prepare__(metacls, name, bases, **kwds):
        return collections.OrderedDict()
     #namespace就是class的__dict__,这个dict类型的对象已经被填充了相应的值
     def __new__(cls, name, bases, namespace, **kwds):
        result = type.__new__(cls, name, bases, dict(namespace))
        result.members = tuple(namespace)
        return result

class A(metaclass=OrderedClass):
    def one(self): pass
    def two(self): pass
    def three(self): pass
    def four(self): pass
print(A.members)
#('__module__', '__qualname__', 'one', 'two', 'three', 'four')