code: def _build_instance_count_and_type_args(self, master_instance_type,
                                              slave_instance_type, num_instances):
          
          params = {
              'Instances.MasterInstanceType' : master_instance_type,
              'Instances.SlaveInstanceType' : slave_instance_type,
              'Instances.InstanceCount' : num_instances,
              }
          return params
docs: Takes a master instance type (string), a slave instance type
          (string), and a number of instances. Returns a comparable dict
          for use in making a RunJobFlow request.