class_docstr: The VolumeRollFinder calculates contract rolls based on when
  volume activity transfers from one contract to another.
class_docstr_tok: ["The","VolumeRollFinder","calculates","contract","rolls","based","on","when","volume","activity","transfers","from","one","contract","to","another","."]
code: def __init__(self, trading_calendar, asset_finder, session_reader):
      self.trading_calendar = trading_calendar
      self.asset_finder = asset_finder
      self.session_reader = session_reader
  
file_path: zipline/zipline/assets/roll_finder.py
imports: from abc import ABCMeta, abstractmethod
  from six import with_metaclass
label_desc: Use image node_id 1 to create a new VolumeRollFinder object from inherited base classes: RollFinder with example: obj = VolumeRollFinder(trading_calendar, asset_finder, session_reader)