code: def _var_key(self, variable):
      # Helper function to get a stable ID and the variable instance mapping.
      return id(variable)
  
imports: import re
  import warnings
  import numpy
  from keras import backend
  from keras import initializers
  from keras import ops
  from keras.optimizers.schedules import learning_rate_schedule
  from keras.saving import serialization_lib
  from keras.utils import tracking
  from keras.utils.naming import auto_name
label_desc: Use image node_id 4 for calling the BaseOptimizer obj's underlying member method code with example usage: obj._var_key(variable) and returns: id