python类在进行实例化的时候，会有一个__dict__属性，里边有可用的实例属性名和值。声明__slots__后，实例就只会含有__slots__里有的属性名。
# coding: utf-8 class a(object): x = 1 def __init__(self): self.y = 2 a = a()print a.__dict__print(a.x, a.y)a.x = 10a.y = 10print(a.x, a.y) class b(object): __slots__ = ('x', 'y') x = 1 z = 2 def __init__(self): self.y = 3 # self.m = 5 # 这个是不成功的 b = b()# print(b.__dict__)print(b.x, b.z, b.y)# b.x = 10# b.z = 10b.y = 10print(b.y) class c(object): __slots__ = ('x', 'z') x = 1 def __setattr__(self, name, val): if name in c.__slots__: object.__setattr__(self, name, val) def __getattr__(self, name): return value of %s % name c = c()print(c.__dict__)print(c.x)print(c.y)# c.x = 10c.z = 10c.y = 10print(c.z, c.y)c.z = 100print(c.z)
{'y': 2}(1, 2)(10, 10)(1, 2, 3)10value of __dict__1value of y(10, 'value of y')100