看python社区大妈组织的内容里边有一篇讲python内存优化的，用到了__slots__。然后查了一下，总结一下。感觉非常有用

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 = 10 a.y = 10 print(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 = 10 b.y = 10 print(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 = 10 c.z = 10 c.y = 10 print(c.z, c.y) c.z = 100 print(c.z)

{'y': 2} (1, 2) (10, 10) (1, 2, 3) 10 Value of __dict__ 1 Value of y (10, 'Value of y') 100