Python-сообщество

class commonClass(object):
   def __init__(self):
      pass

   def method(self):
      pass

class subClass(commonClass):
   def __init__(self):
      pass

   def otherMethod(self):
      pass

class commonClass(object):
    def __init__(self):
        self.x = 1

    def method(self):
        print 'one'

class subClass(commonClass):
    def __init__(self):
        pass

    def otherMethod(self):
        print 'other'

def to_sub(obj, Sub):
    buf = Sub()
    objd = obj.__dict__
    for key in objd:
        setattr(buf, key, objd[key])
    return buf

a = commonClass()
a = to_sub(a, subClass)
a.otherMethod()

class commonClass(object):
    def __getstate__(self):
        return dict(foo = self.foo)

class subClass(commonClass):
    def __setstate__(self, state):
        self.foo = state['foo']

>>> object = commonClass()
>>> object.otherMethod()
Traceback (most recent call last):
...
AttributeError: 'commonClass' object has no attribute 'otherMethod'
>>> subClass.otherMethod(object)
Traceback (most recent call last):
...
TypeError: unbound method otherMethod() must be called with subClass instance as first argument (got commonClass instance instead)
>>> isinstance(object, commonClass)
True
>>> isinstance(object, subClass)
False
>>> object.__class__ = subClass
>>> object.otherMethod()
>>> isinstance(object, commonClass)
True
>>> isinstance(object, subClass)
True