class CustomCallback(keras.callbacks.Callback):
   def on_train_begin(self, logs={}):
   return
   def on_train_end(self, logs={}):
   return
   def on_epoch_begin(self, epoch, logs={}):
   return
   def on_epoch_end(self, epoch, logs={}):
   return
   def on_batch_begin(self, batch, logs={}):
   return
   def on_batch_end(self, batch, logs={}):
   return