log an error message:
        :param exc: exception message

def error(self, exc):
        """
        log an error message:
        :param exc: exception message
        """
        msg = 'trying to execute a step in the environment: \n' \
              '           - Exception: %s' % exc
        if self.logger is not None:
            self.logger.error(msg)
        self.by_console('      ERROR - %s' % msg)