code: def _lookup_key_index(self, key):
      distance, index = self._get_k_nearest_neighbors_indices([key], 1)
      if (
          distance != [[]]
          and distance[0][0] <= self.key_error_threshold
      ):
          return index
      return None
  
imports: import os
  import pickle
  import numpy
label_desc: Use image node_id 9 for calling the AnnoyDictionary obj's underlying member method code with example usage: obj._lookup_key_index(key) and returns: None, index