屬性訪問 property

class C:
    def __init__(self, size=10):
        self.size = size

    def getSize(self):
        return self.size

    def setSize(self, value):
        self.size = value

    def delSize(self):
        del self.size

    x = property(getSize, setSize, delSize)


c = C()
c.x = 1
print
 
(c.size)

定義一個矩形

class Rectangle():
    def __init__(self, width=0, hight=0):
        self.width = width
        self.hight = hight

    def __setattr__(self, name, value):
        if name == 'Square':
            self.hight = value
            self.width = value
        else:
            super().__setattr__
 
(name, value)

    def getArea(self):
        return self.width * self.hight

r1 = Rectangle(3,6)
print(r1.getArea())
r1.Square =10
print(r1.getArea())

如果不使用super()訪問基類的方法，就會陷入死迴圈

描述符：將某種特殊型別的類的例項指派給另一個類的屬性

練習：要求定義一個溫度類，然後定義兩個描述符類用於描述攝氏度和華氏度兩個屬性。要求兩個屬性會自動進行轉換。

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()
temp.cel = 30
print(temp.fah)
print('*')
temp.fah = 100
print(temp.cel)

輸出結果是

86.0
*
37.77777777777778

能夠實現華氏溫度和攝氏溫度的互相轉換