课时45：魔法方法：属性访问

>>> class C:
    def __init__(self):
        self.x = 'X-man'

        
>>> c = C()
>>> c.x
'X-man'
>>> getattr(c,'x','木有这个属性')
'X-man'
>>> getattr(c,'y','木有这个属性')
'木有这个属性'
>>> setattr(c,'y','Yellow')
>>> getattr(c,'y','木有这个属性')
'Yellow'
>>> delattr(c,'x')
>>> c.x
Traceback (most recent call last):
  File "<pyshell#11>", line 1, in <module>
    c.x
AttributeError: 'C' object has no attribute 'x'

>>> 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
10
>>> c.x = 12
>>> c.x
12
>>> c.size
12
>>> del c.x
>>> c.size
Traceback (most recent call last):
  File "<pyshell#29>", line 1, in <module>
    c.size
AttributeError: 'C' object has no attribute 'size'

__getattr__(self, name)             定义当用户试图获取一个不存在的属性时的行为
__getattribute__(self, name)      　定义当该类的属性被访问时的行为
__setattr__(self, name, value)    　定义当一个属性被设置时的行为
__delattr__(self, name)             定义当一个属性被删除时的行为

class C:
    def __getattribute__(self, name):
        print('getattribute')
        # 使用 super() 调用 object 基类的 __getattribute__ 方法
        return super().__getattribute__(name)

    def __setattr__(self, name, value):
        print('setattr')
        super().__setattr__(name, value)

    def __delattr__(self, name):
        print('delattr')
        super().__delattr__(name)

    def __getattr__(self, name):
        print('getattr')

>>> c = C()
>>> c.x
getattribute
getattr
>>> c.x = 1
setattr
>>> c.x
getattribute
1
>>> del c.x
delattr
>>> setattr(c,'y','Yellow')
setattr

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

    def __setattr__(self, name, value):
        if name == 'square':
            self.width = value
            self.height = value
        else:
            self.name = value

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

>>> r1 = Rectangle(4,5)
Traceback (most recent call last):
  File "<pyshell#0>", line 1, in <module>
    r1 = Rectangle(4,5)
  File "C:\Users\14158\Desktop\lalallalalal.py", line 3, in __init__
    self.width = width
  File "C:\Users\14158\Desktop\lalallalalal.py", line 11, in __setattr__
    self.name = value
  File "C:\Users\14158\Desktop\lalallalalal.py", line 11, in __setattr__
    self.name = value
  File "C:\Users\14158\Desktop\lalallalalal.py", line 11, in __setattr__
    self.name = value
  [Previous line repeated 987 more times]
  File "C:\Users\14158\Desktop\lalallalalal.py", line 7, in __setattr__
    if name == 'square':
RecursionError: maximum recursion depth exceeded in comparison

        else:
            super().__setattr__(name,value)

>>> r1 = Rectangle(4,5)
>>> r1.getArea()
20
>>> r1.square = 10
>>> r1.getArea()
100

        else:
            self.__dict__[name] = value