shared.py

def shared(**kwargs):
    class Shared(object):
        @classmethod
        def get_shared_data(cls):
            return kwargs
    return Shared


BaseSharedStuff = shared(username="user", password="pass")


class RemoteThingy(BaseSharedStuff):

    def __new__(cls, *args, **kwargs):
        self = super(RemoteThingy, cls).__new__(cls, *args, **kwargs)
        self.__dict__.update(self.get_shared_data())
        return self


class RemoteUser(RemoteThingy):

    def __init__(self, account_id):
        # no __init__ super call!
        self.account_id = account_id


assert RemoteUser(12345).username == "user"
assert RemoteUser(12345).account_id == 12345