docs: def _validate(self):
          """Checks that the db-file is ok
  
          Returns:
              True if OK, False if not.
              """
          probably_good_to_go = True
          sheet = self.table
          identity = self.db_sheet_cols.id
  
          # check if you have unique srnos
          id_col = sheet.loc[:, identity]
          if any(id_col.duplicated()):
              warnings.warn(
                  "your database is corrupt: duplicates"
                  " encountered in the srno-column")
              logger.debug("srno duplicates:\n" + str(
                  id_col.duplicated()))
              probably_good_to_go = False
          return probably_good_to_go