class_docstr: Metaclass for DataSets
  
  Supplies name and dataset information to Column attributes.
code: def columns(self):
      return frozenset(
          getattr(self, colname) for colname in self._column_names
      )
  
imports: from functools import total_ordering
  from six import iteritems, with_metaclass
  from catalyst.pipeline.classifiers import Classifier, Latest
  from catalyst.pipeline.factors import Factor, Latest
  from catalyst.pipeline.filters import Filter, Latest
  from catalyst.pipeline.sentinels import NotSpecified
  from catalyst.pipeline.term import AssetExists, LoadableTerm, validate_dtype
  from catalyst.utils.input_validation import ensure_dtype
  from catalyst.utils.numpy_utils import NoDefaultMissingValue
  from catalyst.utils.preprocess import preprocess
label_desc: Use image node_id 2 for calling the DataSetMeta obj's underlying member method code with example usage: obj.columns() and returns: frozenset