code: def _reset_when(self, ddate=datetime.min):
      self._when = self._rstwhen
      self._dtwhen = self._dwhen = None
  
      self._lastcall = ddate
  
file_path: backtrader/backtrader/timer.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  import bisect
  import collections
  from datetime import date, datetime, timedelta
  from itertools import islice
  from .feed import AbstractDataBase
  from .metabase import MetaParams
  from .utils import date2num, num2date
  from .utils.py3 import integer_types, range, with_metaclass
  from .utils import TIME_MAX
label_desc: Use image node_id 3 for calling the Timer obj's underlying member method code with example usage: obj._reset_when(ddate) without return types