Issues a payment of money from your account to a Worker.  To
        be eligible for a bonus, the Worker must have submitted
        results for one of your HITs, and have had those results
        approved or rejected. This payment happens separately from the
        reward you pay to the Worker when you approve the Worker's
        assignment.  The Bonus must be passed in as an instance of the
        Price object.

def grant_bonus(self, worker_id, assignment_id, bonus_price, reason):
        """
        Issues a payment of money from your account to a Worker.  To
        be eligible for a bonus, the Worker must have submitted
        results for one of your HITs, and have had those results
        approved or rejected. This payment happens separately from the
        reward you pay to the Worker when you approve the Worker's
        assignment.  The Bonus must be passed in as an instance of the
        Price object.
        """
        params = bonus_price.get_as_params('BonusAmount', 1)
        params['WorkerId'] = worker_id
        params['AssignmentId'] = assignment_id
        params['Reason'] = reason

        return self._process_request('GrantBonus', params)