code: def __init__(self):
      super(ReturnsAnalyzerBase, self).__init__()
      self.__event = observer.Event()
      self.__portfolioReturns = None
  
imports: import math
  from pyalgotrade import stratanalyzer
  from pyalgotrade import observer
  from pyalgotrade import dataseries
label_desc: Use image node_id 1 to create a new ReturnsAnalyzerBase object from inherited base classes: stratanalyzer with example: obj = ReturnsAnalyzerBase()