docstr: Logging function fot this strategy
docstr_tok: ["Logging","function","fot","this","strategy"]
code: def log(self, txt, dt=None):
      """Logging function fot this strategy"""
      dt = dt or self.data.datetime[0]
      if isinstance(dt, float):
          dt = bt.num2date(dt)
      print("%s, %s" % (dt.isoformat(), txt))
  
file_path: backtrader/samples/observers/observers-orderobserver.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import datetime
  import backtrader
  import backtrader.feeds
  import backtrader.indicators
  from orderobserver import OrderObserver
label_desc: Use image node_id 1 for calling the MyStrategy obj's underlying member method code with example usage: obj.log(txt, dt) without return types