python - 我可以切换这个函数 vanilla.count()

Question

我想知道是否可以编写 count(vanilla) 而不是 vanilla.count() ？它类似于 len(list) 但我想做 len(myclass)。是否可以在我的用户定义类上实现这样的功能？下面只是我写的一个虚拟类来问这个问题。谢谢。

    class IceCream():
    # Flavor is a string
    # Toppings is a list of strings
    def __init__(self, flavor, toppings, ):
        self.name = flavor
        self.toppings = toppings
    # Return the number of toppings
    def count(self):
        return len(self.toppings)
    def __str__(self):
        return "{0} flavor ice cream".format(self.name)


vanillaToppings = ['chocolate chips', 'fudge', 'penuts']
vanilla = IceCream('Vanilla', vanillaToppings)
print(vanilla, 'with', vanilla.count(), 'kind of toppings!')
# Is it possible? If so, how do I do it?
# print(vanilla, 'with', len(vanilla), 'kind of toppings!')

Answer 1

如何利用 python 的 special methods 之一？ : __len__ ？

Called to implement the built-in function len(). Should return the length of the object, an integer >= 0.

class IceCream():
    # Flavor is a string
    # Toppings is a list of strings
    def __init__(self, flavor, toppings):
        self.name = flavor
        self.toppings = toppings

    # Return the number of toppings
    def __len__(self):
        return len(self.toppings)

    def __str__(self):
        return "{0} flavor ice cream".format(self.name)


vanillaToppings = ['chocolate chips', 'fudge', 'penuts']
vanilla = IceCream('Vanilla', vanillaToppings)
print(vanilla, 'with', len(vanilla), 'kind of toppings!')

我猜想 count 和 length 的意思在这种情况下可以互换，所以为什么不用熟悉的东西呢？