[知识点备忘] 第064讲：类和对象（VII）

class C:
    def __init__(self,x):
        self.__x=x
    def set_x(self,x):
        self.__x=x
    def get_x(self):
        print(self.__x)

        
c=C(250)
c.__x
Traceback (most recent call last):
  File "<pyshell#249>", line 1, in <module>
    c.__x
AttributeError: 'C' object has no attribute '__x'
c.get_x()
250
c.set_x(520)
c.get_x()
520
c.__dict__
{'_C__x': 520}
c._C__x
520
class D:
    def __func(self):
        print("hello fishc.")

        
d=D()
d.__func()
Traceback (most recent call last):
  File "<pyshell#260>", line 1, in <module>
    d.__func()
AttributeError: 'D' object has no attribute '__func'. Did you mean: '_D__func'?
d._D__func()
hello fishc.
c.__y=250
c.__dict__
{'_C__x': 520, '__y': 250}

class C:
    def __init__(self,x):
        self.x=x

        
c=C(250)
c.x
250
c.__dict__
{'x': 250}
c.y=520
c.__dict__
{'x': 250, 'y': 520}
c.__dict__['z']=666
c.__dict__
{'x': 250, 'y': 520, 'z': 666}
c.z
666
class C:
    __slots__=["x","y"]
    def __init__(self,x):
        self.x=x

        
c=C(250)
c.x
250
c.y=520
c.y
520
c.z=666
Traceback (most recent call last):
  File "<pyshell#287>", line 1, in <module>
    c.z=666
AttributeError: 'C' object has no attribute 'z'
class D:
    __slots__=["x","y"]
    def __init__(self,x,y,z):
        self.x=x
        self.y=y
        self.z=z

        
d=D(3,4,5)
Traceback (most recent call last):
  File "<pyshell#295>", line 1, in <module>
    d=D(3,4,5)
  File "<pyshell#294>", line 6, in __init__
    self.z=z
AttributeError: 'D' object has no attribute 'z'
class E(C):
    pass

e=E(250)
e.x
250
e.y=520
e.y
520
e.z=666
e.__slots__
['x', 'y']
e.__dict__
{'z': 666}

#私有变量：P147 Name Mangling，
# 定义方法：__变量名，外部访问方法：_类名__变量名

#舍得之道：对象中灵活添加的属性，是用字典存储，字典效率快的背后是占用了大量内存（空间换时间）
class C:
    def __init__(self, x):
        self.x = x

c = C(250)
print(c.__dict__)
#{'x': 250}
c.__dict__['y'] = 520
print(c.__dict__)
#{'x': 250, 'y': 520}

#__slots__：如果已经明确一个类的对象设计出来不会有动态添加属性的需求，可以使用__slots__的类属性避免利用字典存放造成空间浪费
class D:
    __slots__ = ['x', 'y'] #列表中的就是希望的属性名
    def __init__(self, x):
        self.x = x

d = D(10)
d.y = 20
print(d.x, d.y, sep='   ')
try:
    print(d.__dict__)
except AttributeError as e:
    print(e)
#'D' object has no attribute '__dict__'
try:
    d.z = 66
except AttributeError as e:
    print(e)
#'D' object has no attribute 'z'

#类的内部同样不允许创建__slots__不包含的属性
class D:
    __slots__ = ['x', 'y']
    def __init__(self, x, y, z):
        self.x = x
        self.y = y
        self.z = z
# d = D(3, 4, 5)
#AttributeError: 'D' object has no attribute 'z'
#使用__slots__后，对象就会划分一个固定大小的空间来存放指定属性
#__slots__限制动态添加属性，也可以用来防止属性的滥用

#继承在父类的__slots__属性不会在子类中生效
class E(C):
    pass

e = E(3)
e.z = 10
print(e.__dict__)
#{'x': 3, 'z': 10}
print(e.__slots__)
#AttributeError: 'E' object has no attribute '__slots__'

class A:
    def __init__(self,x,y):
        self.__x=x
        self.__y=y