python - creating managed attributes

Question

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

Answer 1

__init__裡進行初始化 來給first_name賦值
這裡使用的self.first_name 是因為要用
@first_name.setter def first_name(self, value):

如果直接使用self._first_name 那就不會進入
@first_name.setter def first_name(self, value):

也就沒有
if not isinstance(value, str): raise TypeError('Expected a string')
的類型檢查。

Answer 2

和java透過getter存取私有變數類似，避免直接存取變量，更規範