def errors(self, value):
        """
        Returns a list of errors with the value. An empty/None return means
        that it's valid.
        """
        if value not in self.values:
            return [Error(self._error_message, code=ERROR_CODE_UNKNOWN)]
        return []
def errors ( self , value ) : if value not in self . values : return [ Error ( self . _error_message , code = ERROR_CODE_UNKNOWN ) ] return [ ]
Returns a list of errors with the value. An empty/None return means
        that it's valid.