code: def on_epoch_begin(self, epoch, logs=None):
      keys = list(logs.keys())
      print(
          "Start epoch {} of training; got log keys: {}".format(
              epoch, keys
          )
      )
  
imports: import numpy
  import keras
label_desc: Use image node_id 3 for calling the CustomCallback obj's underlying member method code with example usage: obj.on_epoch_begin(epoch, logs) without return types