code: def initialize_subperiod_divider(self):
      self.calculate_performance()
  
      # Initialize a subperiod divider to stash the current performance
      # values. Current period starting values are set to equal ending values
      # of the previous subperiod
      self.subperiod_divider = SubPeriodDivider(
          prev_returns=self.returns,
          prev_pnl=self.pnl,
          prev_cash_flow=self.cash_flow,
          curr_starting_value=self.ending_value,
          curr_starting_cash=self.ending_cash,
      )
  
imports: from __future__ import division
  import logbook
  import numpy
  from collections import namedtuple
  from catalyst.assets import Future
  from six import itervalues, iteritems
  import catalyst.protocol
  from catalyst.constants import LOG_LEVEL
label_desc: Use image node_id 7 for calling the PerformancePeriod obj's underlying member method code with example usage: obj.initialize_subperiod_divider() without return types