code: def get_scheme_prefix(index, indexes, tagging_scheme):
      if tagging_scheme == TaggingScheme.IO:
          return INSIDE_PREFIX
      elif tagging_scheme == TaggingScheme.BIO:
          if index == indexes[0]:
              return BEGINNING_PREFIX
          return INSIDE_PREFIX
      elif tagging_scheme == TaggingScheme.BILOU:
          if len(indexes) == 1:
              return UNIT_PREFIX
          if index == indexes[0]:
              return BEGINNING_PREFIX
          if index == indexes[-1]:
              return LAST_PREFIX
          return INSIDE_PREFIX
      else:
          raise ValueError("Invalid tagging scheme %s" % tagging_scheme)
  
imports: from __future__ import unicode_literals
  from builtins import range
  from enum import Enum, unique
  from snips_nlu.constants import END, SLOT_NAME, START, TEXT
  from snips_nlu.preprocessing import Token, tokenize
  from snips_nlu.result import unresolved_slot
label_desc: Use image node_id 14 for calling a global function with example usage: get_scheme_prefix(index, indexes, tagging_scheme) and returns: INSIDE_PREFIX, INSIDE_PREFIX, BEGINNING_PREFIX, INSIDE_PREFIX, UNIT_PREFIX, BEGINNING_PREFIX, LAST_PREFIX