使用元类，metaclass

• 廖雪峰的博客讲的太好了
• https://www.liaoxuefeng.com/wiki/001374738125095c955c1e6d8bb493182103fac9270762a000/001386820064557c69858840b4c48d2b8411bc2ea9099ba000

class test(object):
    pass
t=test()
t.name='hello'
print t.name    #hello                                                                                                                                
print test.name    #AttributeError: type object 'test' has no attribute 'name'