Cookbook 8.6节有个例子：
http://chimera.labs.oreilly.com/books/1230000000393/ch08.html#_problem_124

class Person:
    def __init__(self, first_name):
        self.first_name = first_name

    # Getter function
    @property
    def first_name(self):
        return self._first_name

    # Setter function
    @first_name.setter
    def first_name(self, value):
        if not isinstance(value, str):
            raise TypeError('Expected a string')
        self._first_name = value

    # Deleter function (optional)
    @first_name.deleter
    def first_name(self):
        raise AttributeError("Can't delete attribute")

有个问题是，为什么__init__里面的是self.first_name而不是self._first_name,他说是

In this example, the entire point of the property is to apply type checking when setting an attribute. Thus, chances are you would also want such checking to take place during initialization. By setting self.first_name, the set operation uses the setter method (as opposed to bypassing it by accessing self._first_name).

我看不明白，求解释一下，多谢