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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def _check_log_level(self, level):
        '''
        Ensures a valid log level

        @param level: the asked for level
        '''
        if level not in list(self.level_dict.keys()):
            self.log_level = 'DEBUG'
            self.logger.warn("Unknown log level '{lev}', defaulting to DEBUG"
                             .format(lev=level))