code: def _n_nodes(self) -> int:
      return self._tree.node_count
  
imports: from __future__ import annotations
  from functools import lru_cache
  import itertools
  from typing import List
  from typing import Set
  from typing import Tuple
  from typing import TYPE_CHECKING
  from typing import Union
  import numpy
label_desc: Use image node_id 10 for calling the _FanovaTree obj's underlying member method code with example usage: obj._n_nodes() and returns: self