Return the default value of a given option
        
        :param opt_name: option name
        :type opt_name: str
        
        :returns: the default value of the option

def get_option_default(self, opt_name):
        """ Return the default value of a given option
        
        :param opt_name: option name
        :type opt_name: str
        
        :returns: the default value of the option
        """
        if not self.has_option(opt_name):
            raise ValueError("Unknow option name (%s)" % opt_name)
        return self._options[opt_name].default