code: def adjust_mod_previous(self, holidays_obj=None):
          
          month = self.month
          new = BusinessDate.adjust_previous(self, holidays_obj)
          if month != new.month:
              new = BusinessDate.adjust_follow(self, holidays_obj)
          self = new
          return self
docs: ajusts to Business Day Convention "Modified Preceding" (not in 2006 ISDA Definitons).