描述器(描述符)

**描述符就是将某种特殊类型的类的实例指派给另一个类的属性**<br />**___get__(self, instance, owner)用于访问属性,它返回属性的值**

set(self, instance, value)将在属性分配操作中调用, 不返回任何内容

delete(self, instance)控制删除,不返回任何内容

自带的 Property

class MyDecriptor:
    def __get__(self, instance, owner):
        print("getting...", instance, owner)
    def __set__(self, instance, value):
        print("setting...", instance, value)
    def __delete__(self, instance):
        print("deleteting...", instance)
class Test:
    x = MyDecriptor()
test = Test()
test.x
test.x = "100"
del test.x
--------------------------------
getting... <__main__.Test object at 0x0316B040> <class '__main__.Test'>
setting... <__main__.Test object at 0x0316B040> 100
deleteting... <__main__.Test object at 0x0316B040>

自已实现 Property

class MyProperty:
    def __init__(self, fget = None, fset = None, fdel = None):
        self.fget = fget
        self.fset = fset
        self.fdel = fdel
    def __get__(self, instance, owner):
        return self.fget(instance) # instance 实例对象
    def __set__(self, instance, value):
        return self.fset(instance, value)
    def __delete__(self, instance):
        return self.fdel(instance)
class Test:
    def __init__(self):
        self._x = None
    def getX(self):
        return self._x
    def setX(self, value):
        self._x = value
    def delX(self):
        del self._x
    x = MyProperty(getX, setX, delX)
test = Test()
test.x = "x-main"
print(test.x) # 用x  取修改了 _x 的值   _x 属于另一个的的属性
print(test._x)
------------------------------------
x-main
x-main

练习要求

先定义一个温度类, 然后定义两个描述符类 用于描述摄氏度和华氏度两个属性 .

要求两个属性会自动进行转换, 也就是说你可以给摄氏度这个属性赋值, 然后打印的华氏度属性是自动转换后的结果

公式: * 1.8 + 32

class Celsius:
    def __init__(self, value = 26.0):
        self.value = float(value)
    def __get__(self, instance, owner):
        return self.value
    def __set__(self, instance, value):
        self.value = float(value)
class Fahrenheit:
    def __get__(self, instance, owner):
        return instance.cel *1.8+32
    def __set__(self, instance, value):
        instance.cel = (float(value) - 32) / 1.8
class Temperature:
    cel = Celsius()
    fah = Fahrenheit()
temp = Temperature()
print(temp.cel)  # 默认是摄氏度
temp.cel = 30    # 修改摄氏度
print(temp.fah)   # 自动转换为华氏度
temp.fah = 100   # 输入华氏度
print(temp.cel)  # 自动转换摄氏度
-------------------------------
26.0
86.0
37.77777777777778