Python附加到派生类定义中的类级别列表

Question

class A (object):
    keywords = ('one', 'two', 'three')

class B (A):
    keywords = A.keywords + ('four', 'five', 'six')

有没有办法把A.keywords改成<thing B derives from>.keywords，有点像super()，但是在__init__/self之前？我不喜欢在定义中重复类名。在

用法：

^{pr2}$

Answer 1

使用元类：

#!/usr/bin/env python
# -*- coding: utf-8 -*-

class Meta(type):
    def __new__(cls, name, bases, attrs):
        new_cls = super(Meta,cls).__new__(cls, name, bases, attrs)
        if hasattr(new_cls, 'keywords'):
            new_cls.keywords += ('1','2')
        return new_cls

class B(object):
    keywords = ('0',)
    __metaclass__= Meta

def main():
    print B().keywords

if __name__ == '__main__':
    main()

Answer 2

是的。当你已经初始化了你的类的时候，使用这个属性来查找基类。否则，您需要改变方法，因为B不知道它的父类。在

class A (object):
    keywords = ('one', 'two', 'three')

class B (A):
    def __init__(self):
        keywords = self.__bases__[0].keywords + ('four', 'five', 'six')

Answer 3

实际上，你可以。编写一个descriptor，检查类的基是否有同名的属性，并将传递的属性添加到其值中。在

class parentplus(object):
    def __init__(self, name, current):
        self.name = name
        self.value = current

    def __get__(self, instance, owner):
        # Find the attribute in self.name in instance's bases
        # Implementation left as an exercise for the reader

class A(object):
    keywords = ('one', 'two', 'three')

class B(A):
    keywords = parentplus('keywords', ('four', 'five', 'six'))