class_docstr: This is a singleton class for RDKit base features.
class_docstr_tok: ["This","is","a","singleton","class","for","RDKit","base","features","."]
code: def get_instance(cls):
      try:
          from rdkit import RDConfig
          from rdkit.Chem import ChemicalFeatures
      except ModuleNotFoundError:
          raise ImportError(
              "This class requires RDKit to be installed."
          )
  
      if not cls._instance:
          fdefName = os.path.join(
              RDConfig.RDDataDir, "BaseFeatures.fdef"
          )
          cls._instance = ChemicalFeatures.BuildFeatureFactory(fdefName)
      return cls._instance
  
imports: import os
  import logging
  from typing import List, Union, Tuple
  import numpy
  from deepchem.utils.typing import RDKitAtom, RDKitBond, RDKitMol
label_desc: Use image node_id 1 for calling the _ChemicalFeaturesFactory obj's underlying member method code with example usage: obj.get_instance(cls) and returns: cls