class_docstr: An EventBasedFilter class is responsible for capturing new values in a :class:`pyalgotrade.dataseries.DataSeries`
  and using an :class:`EventWindow` to calculate new values.
  
  :param dataSeries: The DataSeries instance being filtered.
  :type dataSeries: :class:`pyalgotrade.dataseries.DataSeries`.
  :param eventWindow: The EventWindow instance to use to calculate new values.
  :type eventWindow: :class:`EventWindow`.
  :param maxLen: The maximum number of values to hold.
      Once a bounded length is full, when new items are added, a corresponding number of items are discarded from the
      opposite end. If None then dataseries.DEFAULT_MAX_LEN is used.
  :type maxLen: int.
code: def getEventWindow(self):
      return self.__eventWindow
  
file_path: pyalgotrade/pyalgotrade/technical/__init__.py
imports: from pyalgotrade.utils import collections
  from pyalgotrade import dataseries
label_desc: Use image node_id 4 for calling the EventBasedFilter obj's underlying member method code with example usage: obj.getEventWindow() and returns: self