动态非常灵活, 创建一个class后, 给实例绑定一个属性:
>>> class Bird: ... pass ... >>> s = Bird() >>> s.name = ‘bob‘ >>> s.name bob
也可以给实例绑定一个方法, 但是这对另一个实例是无效的:
>>> def age(self,age): ... self.age = age ... >>> from types import MethodType >>> >>> s.age = MethodType(age,s,Bird) >>> s.age(0.5) >>> print s.age 0.5 >>> s2 = Bird() >>> s2.age(1) Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: Bird instance has no attribute ‘age‘
为了给所有实例都绑定方法，可以给class绑定方法, 绑定后所以属于该类的实例均可调用:
>>> def is_running(self): ... print ‘running...‘ ... >>> Bird.is_running = MethodType(is_running, None, Bird) >>> s3 = Bird() >>> s3.is_running() running... >>> s2.is_running() running...
__slots__
如果我们需要限制class的属性怎么办? 比如说我们定义一个Person类, 只允许对Person实例添加 name age属性, 不允许添加gender属性! 所以我们需要使用 __slots__
>>> class Person(object): ... __slots__ = (‘name‘,‘age‘) ... >>> s = Person() >>> s.name = ‘Johb‘ >>> s.age = ‘22‘ >>> s.gender = ‘male‘ Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: ‘Person‘ object has no attribute ‘gender‘
但是对于Person的子类是不起作用的, 除非子类也定义 __slots__
>>> class SuperPerson(Person): ... pass ... >>> s = SuperPerson() >>> s.aaaaa = ‘no restriction‘ >>> s.aaaaa ‘no restriction‘
注意: 因为Python的历史遗留问题, 在2.x版本中, 如果类后面没有跟object __slots__的限制将会无效
>>> class Person: ... __slots__=(‘name‘,‘age‘) ... >>> s.gender = ‘male‘ >>> s.gender ‘male‘
原文：http://www.cnblogs.com/zhanhg/p/4395895.html