code: def put_group_policy(self, group_name, policy_name, policy_json):
          
          params = {'GroupName' : group_name,
                    'PolicyName' : policy_name,
                    'PolicyDocument' : policy_json}
          return self.get_response('PutGroupPolicy', params, verb='POST')
docs: Adds or updates the specified policy document for the specified group.
  
          :type group_name: string
          :param group_name: The name of the group the policy is associated with.
  
          :type policy_name: string
          :param policy_name: The policy document to get.
  
          :type policy_json: string
          :param policy_json: The policy document.