code: def start(self):
      header = [
          "Len",
          "Name",
          "RollName",
          "Datetime",
          "WeekDay",
          "Open",
          "High",
          "Low",
          "Close",
          "Volume",
          "OpenInterest",
      ]
      print(", ".join(header))
  
file_path: backtrader/samples/rollover/rollover.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import argparse
  import bisect
  import calendar
  import datetime
  import backtrader
label_desc: Use image node_id 1 for calling the TheStrategy obj's underlying member method code with example usage: obj.start() without return types