docs: def get_date_bounds(self):
          """
          Return the upper and lower bounds along
          with operators that are needed to do an 'in range' test.
          Useful for SQL commands.
  
          Returns
          -------
          tuple: (`str`, `date`, `str`, `date`)
                  (date_gt, start, date_lt, end)
          e.g.:
                  ('>=', start_date, '<', end_date)
          """
          start = end = None
          date_gt = '>='
          date_lt = '<='
          if self:
              if self.start:
                  start = self.start
              if self.end:
                  end = self.end
              if self.startopen:
                  date_gt = '>'
              if self.endopen:
                  date_lt = '<'
  
          return date_gt, start, date_lt, end