code: def modify_instance_groups(self, instance_group_ids, new_sizes):
          
          if type(instance_group_ids) != types.ListType:
              instance_group_ids = [instance_group_ids]
          if type(new_sizes) != types.ListType:
              new_sizes = [new_sizes]
  
          instance_groups = zip(instance_group_ids, new_sizes)
  
          params = {}
          for k, ig in enumerate(instance_groups):
              # could be wrong - the example amazon gives uses
              # InstanceRequestCount, while the api documentation
              # says InstanceCount
              params['InstanceGroups.member.%d.InstanceGroupId' % (k+1) ] = ig[0]
              params['InstanceGroups.member.%d.InstanceCount' % (k+1) ] = ig[1]
  
          return self.get_object('ModifyInstanceGroups', params,
                                 ModifyInstanceGroupsResponse, verb='POST')
docs: Modify the number of nodes and configuration settings in an
          instance group.
  
          :type instance_group_ids: list(str)
          :param instance_group_ids: A list of the ID's of the instance
              groups to be modified
              
          :type new_sizes: list(int)
          :param new_sizes: A list of the new sizes for each instance group