code: def __init__(self):
      # To control operation entries
      self.orderid = None
      self.qty1 = self.p.qty1
      self.qty2 = self.p.qty2
      self.upper_limit = self.p.upper
      self.lower_limit = self.p.lower
      self.up_medium = self.p.up_medium
      self.low_medium = self.p.low_medium
      self.status = self.p.status
      self.portfolio_value = self.p.portfolio_value
  
      # Signals performed with PD.OLS :
      self.transform = btind.OLS_TransformationN(
          self.data0, self.data1, period=self.p.period
      )
      self.zscore = self.transform.zscore
  
file_path: backtrader/contrib/samples/pair-trading/pair-trading.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import argparse
  import datetime
  import backtrader
  import backtrader.feeds
  import backtrader.indicators
label_desc: Use image node_id 3 to create a new PairTradingStrategy object from inherited base classes: bt with example: obj = PairTradingStrategy()