code: def _feature_definitions(self):
      if not self._features_dict:
          self._features_dict = {}
          self._primitives_dict = {}
  
          for feature in self.feature_list:
              self._serialize_feature(feature)
  
          primitive_number = 0
          primitive_id_to_key = {}
          for name, feature in self._features_dict.items():
              primitive = feature["arguments"].get("primitive")
              if primitive:
                  primitive_id = id(primitive)
                  if primitive_id not in primitive_id_to_key.keys():
                      # Primitive we haven't seen before, add to dict and increment primitive_id counter
                      # Always use string for keys because json conversion results in integer dict keys
                      # being converted to strings, but integer dict values are not.
                      primitives_dict_key = str(primitive_number)
                      primitive_id_to_key[
                          primitive_id
                      ] = primitives_dict_key
                      self._primitives_dict[
                          primitives_dict_key
                      ] = serialize_primitive(primitive)
                      self._features_dict[name]["arguments"][
                          "primitive"
                      ] = primitives_dict_key
                      primitive_number += 1
                  else:
                      # Primitive we have seen already - use existing primitive_id key
                      key = primitive_id_to_key[primitive_id]
                      self._features_dict[name]["arguments"][
                          "primitive"
                      ] = key
  
      return self._features_dict, self._primitives_dict
  
file_path: featuretools/featuretools/feature_base/features_serializer.py
imports: import json
  from featuretools.primitives.utils import serialize_primitive
  from featuretools.utils.s3_utils import get_transport_params, use_smartopen_features
  from featuretools.utils.wrangle import _is_s3, _is_url
  from featuretools.version import FEATURES_SCHEMA_VERSION
  from featuretools.version import __version__
label_desc: Use image node_id 4 for calling the FeaturesSerializer obj's underlying member method code with example usage: obj._feature_definitions() and returns: self,  self