code: def __mapPos(self, t):
      assert t >= -1 * self.__lookBack and t <= self.__lookForward
      return t + self.__lookBack
  
imports: import numpy
  import matplotlib.pyplot
  from six.moves import xrange
  from pyalgotrade.technical import roc
  from pyalgotrade import dispatcher
label_desc: Use image node_id 2 for calling the Event obj's underlying member method code with example usage: obj.__mapPos(t) and returns: unknown