python - 如何只允许特定类的元素成为可迭代的元素(对于自定义类)

Question

在我的例子中，我想定义一个自定义类(称为 WordTuple)，它是元组类的子类。此自定义元组的元素必须全部属于另一个自定义类(称为 Word)。

我知道这个问题(How to make an iterable class in Python in which only a specific type is allowed to be the element?)是相似的，但答案不是我要找的，我也不是很清楚。

class Word(str):
    pass

class WordTuple(tuple):
    # Here whatever is necessary for the elements of this particular tuple
    # to be all members of the class 'Word'
    pass

Answer 1

因为元组是不可变的，所以您只需要在创建元组时验证对象。您可以在自定义中执行此操作 __new__ method :

class WordTuple(tuple):
    def __new__(cls, *objs):
        if not all(isinstance(o, Word) for o in objs):
            raise TypeError('WordTuple can only contain Word instances')
        return super().__new__(cls, objs)

演示:

>>> WordTuple('a', 'b')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in __new__
TypeError: WordTuple can only contain Word instances
>>> WordTuple(Word('a'), Word('b'))
('a', 'b')