Question

我想从类继承链的各个方面读取每个类的属性。

类似以下内容：

class Base(object):
    def smart_word_reader(self):
        for word in self.words:
            print(word)

class A(Base):
    words = ['foo', 'bar']

class B(A):
    words = ['baz']

if __name__ == '__main__':
    a = A()
    a.smart_word_reader()  # prints foo, bar as expected
    b = B()
    b.smart_word_reader()  # prints baz - how I can I make it print foo, bar, baz?

很显然，每个words属性都应该覆盖其他属性。我该如何做类似的事情，让我从继承链中的每个类中读取words属性？

有没有更好的方法可以解决这个问题？

奖励指向可以与多个继承链配合使用的事物（呈菱形，并且所有内容都从Base继承）。

Answer 1

我想您可以手动对mro进行内部检查，其效果如下：

In [8]: class Base(object):
   ...:     def smart_word_reader(self):
   ...:         for cls in type(self).mro():
   ...:             for word in getattr(cls, 'words', ()):
   ...:                 print(word)
   ...:
   ...: class A(Base):
   ...:     words = ['foo', 'bar']
   ...:
   ...: class B(A):
   ...:     words = ['baz']
   ...:

In [9]: a = A()

In [10]: a.smart_word_reader()
foo
bar

In [11]: b = B()

In [12]: b.smart_word_reader()
baz
foo
bar

或者以reversed的顺序：

In [13]: class Base(object):
    ...:     def smart_word_reader(self):
    ...:         for cls in reversed(type(self).mro()):
    ...:             for word in getattr(cls, 'words', ()):
    ...:                 print(word)
    ...:
    ...: class A(Base):
    ...:     words = ['foo', 'bar']
    ...:
    ...: class B(A):
    ...:     words = ['baz']
    ...:

In [14]: a = A()

In [15]: a.smart_word_reader()
foo
bar

In [16]: b = B()

In [17]: b.smart_word_reader()
foo
bar
baz

或更复杂的模式：

In [21]: class Base(object):
    ...:     def smart_word_reader(self):
    ...:         for cls in reversed(type(self).mro()):
    ...:             for word in getattr(cls, 'words', ()):
    ...:                 print(word)
    ...:
    ...: class A(Base):
    ...:     words = ['foo', 'bar']
    ...:
    ...: class B(Base):
    ...:     words = ['baz']
    ...:
    ...: class C(A,B):
    ...:     words = ['fizz','pop']
    ...:

In [22]: c = C()

In [23]: c.smart_word_reader()
baz
foo
bar
fizz
pop

In [24]: C.mro()
Out[24]: [__main__.C, __main__.A, __main__.B, __main__.Base, object]

Answer 2

我将smart_word_reader设为classmethod，然后在reversed(cls.__mro__)上进行迭代。

class Base:
    @classmethod
    def smart_word_reader(cls):
        the_words = (word for X in reversed(cls.__mro__)
                          for word in vars(X).get('words', []))
        print('\n'.join(the_words))

演示：

>>> a = A()
>>> b = B()
>>> a.smart_word_reader()
foo
bar
>>> b.smart_word_reader()
foo
bar
baz

修改

细微的错误：我们不希望getattr（考虑class C(B): pass）在子类中查找缺少的属性。将getattr的呼叫更改为vars(X).get('words', [])。

在实例方法中从父级访问类属性

2 个答案: