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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 subset(self, service=None):
 """Subset the dataset. Open the remote dataset and get a client for talking to ``service``. Parameters service : str, optional The name of the service for subsetting the dataset. Defaults to 'NetcdfSubset' or 'NetcdfServer', in that order, depending on the services listed in the catalog. Returns ------- a client for communicating using ``service`` """

        if service is None:
            for serviceName in self.ncssServiceNames:
                if serviceName in self.access_urls:
                    service = serviceName
                    break
            else:
                raise RuntimeError('Subset access is not available for this dataset.')
        elif service not in self.ncssServiceNames:
            raise ValueError(service + ' is not a valid service for subset. Options are: '
                             + ', '.join(self.ncssServiceNames))

        return self.access_with_service(service)