def increment(self, key, amount=1):
        """
        Increment one value in the object. Note that this happens immediately:
        it does not wait for save() to be called
        """
        payload = {
            key: {
                '__op': 'Increment',
                'amount': amount
                }
            }
        self.__class__.PUT(self._absolute_url, **payload)
        self.__dict__[key] += amount