code: def keys(self):
          
          return set(
              row[self._keycol] for row in self._connection.execute(
                  """SELECT DISTINCT {} FROM {} ORDER BY {} ASC;""".format(
                      self.selkeycol,
                      self.table,
                      self._keycol
                  )
              )
          )
docs: D.keys() -> a set-like object providing a view on D's keys