code: def _validate_explicit_consumer_groups(cls, val):
          
          assert isinstance(val, dict)
          for consumer_group, topics in iteritems(val):
              assert isinstance(consumer_group, string_types)
              # topics are optional
              assert isinstance(topics, dict) or topics is None
              if topics is not None:
                  for topic, partitions in iteritems(topics):
                      assert isinstance(topic, string_types)
                      # partitions are optional
                      assert isinstance(partitions, (list, tuple)) or partitions is None
                      if partitions is not None:
                          for partition in partitions:
                              assert isinstance(partition, int)
docs: Validate any explicitly specified consumer groups.
  
          While the check does not require specifying consumer groups,
          if they are specified this method should be used to validate them.
  
          val = {'consumer_group': {'topic': [0, 1]}}