设置描述符的默认（初始）值

Question

假设我们得到以下代码：

class NonNegative():
    def __set_name__(self, owner, name):
        self.name = name

    def __get__(self, instance, owner):
        if instance is None:
            return self
        return instance.__dict__[self.name]

    def __set__(self, instance, value):
        instance.__dict__[self.name] = value

class Person:
    fingerCount = NonNegative()
    eyesCount = NonNegative()
    def __init__(self, name):
        self.name = name

p = Person("name")
print(p.fingerCount)    <----- I want a default value printed here, instead of a KeyError
print(p.eyesCount)      <-----                 ------ | | ------

我将如何分别为fingerCount和eyesCount分配默认（初始）值？

这样我就不必做：

p = Person("name")
p.fingerCount = 10
p.eyesCount = 2
print(p.fingerCount)  # output: 10   
print(p.eyesCount)    # output: 2

，但是可以这样做：

p = Person("name")
print(p.fingerCount)  # output: 10   
print(p.eyesCount)    # output: 2

Answer 1

将默认值传递给__init__方法，当instance.__dict__[self.name]不存在时，将其保存以供使用。

Answer 2

用于更静态的硬编码解决方案