code: def get_canonical_key_id(self, key_id):
          
          shard_num = self.get_shard_num_by_key_id(key_id)
          return self._canonical_keys[shard_num]
docs: get_canonical_key_id is used by get_canonical_key, see the comment
          for that method for more explanation.
  
          Keyword arguments:
          key_id -- the key id (e.g. '12345')
  
          returns the canonical key id (e.g. '12')