code: def prenext(self):
      self._daycount()
  
      tm = self.data.datetime.time()
      if self._barisvalid(tm):
          self.pvol[tm] = self.data.volume[0]
          self.vcount[tm] += 1
  
file_path: backtrader/samples/relative-volume/relvolbybar.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import collections
  import datetime
  import math
  import backtrader
label_desc: Use image node_id 5 for calling the RelativeVolumeByBar obj's underlying member method code with example usage: obj.prenext() without return types