code: def _unique_hierarchical_string(self):
          
          t = datetime.now()
          return '%s/%s/%s/%s/%s/%s/%s' % (t.year, t.month, t.day, t.hour,
                                           t.minute, t.second, t.microsecond)
docs: Returns:
              str: a representation of time such as::
  
                  '2014/2/23/15/26/8/9877978'
  
          The last part (microsecond) is needed to avoid duplicates in
          rapid-fire transactions e.g. ``> 1`` edition.