内置装饰器二：@property

property 装饰器的作用

property 装饰器将方法包装成属性，将私有属性公有化，此属性只能被读取。相当于实现get方法的对象

class People:
    def __init__(self, identity_number):
        self._identity_number = identity_number

    @property  # 只读
    def age(self):
        return self._age

    @age.setter  # 写
    def age(self, value):
        if not isinstance(value, int):
            raise ValueError("age must be an integer!")
        if value < 0:
            raise ValueError("age must more than 0")
        self._age = value

    @age.deleter  # 删除
    def age(self):
        del self._age

    @property
    def get_identity_number(self):
        return self._identity_number
    

#In [22]: p = People(123456)

#In [23]: p.age = 18

# In [24]: p.age
# Out[24]: 18

# In [25]: del p.age

# In [26]: p.age
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-26-3523b116dc0e> in <module>()
----> 1 p.age

<ipython-input-21-de21f31a52ce> in age(self)
      5     @property  # 只读
      6     def age(self):
----> 7         return self._age
      8
      9     @age.setter  # 写

AttributeError: 'People' object has no attribute '_age'

# In [27]: p.age = 18

# In [28]: p.age = 18.6
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-28-8a03211dcd49> in <module>()
----> 1 p.age = 18.6

<ipython-input-21-de21f31a52ce> in age(self, value)
     10     def age(self, value):
     11         if not isinstance(value, int):
---> 12             raise ValueError("age must be an integer!")
     13         if value < 0:
     14             raise ValueError("age must more than 0")

ValueError: age must be an integer!

# In [29]: p.age = '11'
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-29-b6d20eff2848> in <module>()
----> 1 p.age = '11'

<ipython-input-21-de21f31a52ce> in age(self, value)
     10     def age(self, value):
     11         if not isinstance(value, int):
---> 12             raise ValueError("age must be an integer!")
     13         if value < 0:
     14             raise ValueError("age must more than 0")

ValueError: age must be an integer!

# In [30]: p.age = -1
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-30-47db6d5817ed> in <module>()
----> 1 p.age = -1

<ipython-input-21-de21f31a52ce> in age(self, value)
     12             raise ValueError("age must be an integer!")
     13         if value < 0:
---> 14             raise ValueError("age must more than 0")
     15         self._age = value
     16

ValueError: age must more than 0

# In [31]:

会把成员函数x转换为getter，相当于做了x = property(); x = x.getter(x_get)

• @property表示只读。
• 同时有@property和@x.setter表示可读可写。
• 同时有@property和@x.setter和@x.deleter表示可读可写可删除。

参考资料：https://docs.python.org/3/library/functions.html?highlight=property#property

http://blog.willdx.me/web/面向对象进阶.html