code: def safe_values(self, value):
          
          # TODO: override-able?
          string_val = ""
          if isinstance(value, datetime.date):
              try:
                  string_val = value.strftime('{0}{1}{2}'.format(
                      current_app.config['DATETIME']['DATE_FORMAT'],
                      current_app.config['DATETIME']['SEPARATOR'],
                      current_app.config['DATETIME']['TIME_FORMAT']))
              except RuntimeError as error:
                  string_val = value.strftime('%Y-%m-%d %H:%M:%S')
          elif isinstance(value, bytes):
              string_val = value.decode('utf-8')
          elif isinstance(value, decimal.Decimal):
              string_val = float(value)
          else:
              string_val = value
          return string_val
docs: Parse non-string values that will not serialize