code: def on_start(self, state):
      self.t0 = time.time()
      self.batch_timer.reset(state)
      self.epoch_timer.reset(state)
      self.train_timer.reset(state)
      self.valid_timer.reset(state)
      self.total_timer.reset(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 5 for calling the TimerMetric obj's underlying member method code with example usage: obj.on_start(state) without return types