code: def on_start_validation(self, state):
      super(TimerMetric, self).on_start_validation(state)
      self.update_time(ON_START_VALIDATION, self.batch_timer, state)
  
imports: from __future__ import print_function
  import sys
  import time
  from torchbearer.callbacks import Callback
  import torchbearer
  from torchbearer.metrics import Metric
label_desc: Use image node_id 13 for calling the TimerMetric obj's underlying member method code with example usage: obj.on_start_validation(state) without return types