implement __getattr__ in both class and instance

getattr_test

#!/usr/bin/env python
# -*- coding: utf-8 -*-

class A(object):
    def __init__(self, key):
        print 'A key', key
    
    @classmethod
    def foo(cls):
        print 'A foo'

    def bar(self):
        print 'A bar'

class B(object):
    def __init__(self, key):
        print 'A key', key
    
    @classmethod
    def foo(cls):
        print 'B foo'

    def bar(self):
        print 'B bar'

import random        
def get_random_key():
    return random.choice(['A', 'B'])

class AttrType(type):
    def __init__(cls, name, bases, dict):
        key = get_random_key()
        if key == 'A':
            cls.klass = A
        elif key == 'B':
            cls.klass = B
        
        super(AttrType, cls).__init__(name, bases, dict)

    def __getattr__(cls, name):
        return getattr(cls.klass, name)

class MyClass(object):
    __metaclass__ = AttrType

    def __init__(self, key):
        if key == 'A':
            self.obj = A(key)
        elif key == 'B':
            self.obj = B(key)

    def __getattr__(self, name):
        return getattr(self.obj, name)
        
if __name__ == '__main__':
    MyClass.foo()

    obj = MyClass('A')
    obj.bar()

    obj = MyClass('B')
    obj.bar()