code: def _get_composite_distance_features(distance):
      """
      Return the union of feature names across all components in a composite
      distance specification.
      """
      return list(set(reduce(iadd, [x[0] for x in distance], [])))
  
file_path: turicreate/src/python/turicreate/toolkits/distances/_util.py
imports: from __future__ import print_function
  from __future__ import division
  from __future__ import absolute_import
  import copy
  import array
  import six
  from operator import iadd
  import turicreate
  import sys
label_desc: Use image node_id 5 for calling a global function with example usage: _get_composite_distance_features(distance) and returns: list