code: def next(self):
      txtfields = list()
      txtfields.append("%04d" % len(self))
      txtfields.append(self.data0.datetime.date(0).isoformat())
      txtfields.append("%.2f" % self.data0.open[0])
      txtfields.append("%.2f" % self.data0.high[0])
      txtfields.append("%.2f" % self.data0.low[0])
      txtfields.append("%.2f" % self.data0.close[0])
      txtfields.append("%.2f" % self.data0.volume[0])
      txtfields.append("%.2f" % self.data0.openinterest[0])
      print(",".join(txtfields))
  
      # Single order
      if self.doop == 0:
          if not self.position.size:
              stakevol = (
                  self.data0.volume[0] * self.p.stakeperc
              ) // 100
              print("++ STAKE VOLUME:", stakevol)
              self.buy(size=stakevol)
  
          else:
              self.close()
  
      self.doop += 1
  
file_path: backtrader/samples/volumefilling/volumefilling.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import argparse
  import datetime
  import os.path
  import time
  import sys
  import backtrader
label_desc: Use image node_id 4 for calling the St obj's underlying member method code with example usage: obj.next() without return types