docs: def get_checksums(self, fileset):
          """
          Downloads the MD5 digests associated with the files in the file-set.
          These are saved with the downloaded files in the cache and used to
          check if the files have been updated on the server
  
          Parameters
          ----------
          resource : xnat.ResourceCatalog
              The xnat resource
          file_format : FileFormat
              The format of the fileset to get the checksums for. Used to
              determine the primary file within the resource and change the
              corresponding key in the checksums dictionary to '.' to match
              the way it is generated locally by Arcana.
          """
          if fileset.uri is None:
              raise ArcanaUsageError(
                  "Can't retrieve checksums as URI has not been set for {}"
                  .format(fileset))
          with self:
              checksums = {r['Name']: r['digest']
                           for r in self._login.get_json(fileset.uri + '/files')[
                               'ResultSet']['Result']}
          if not fileset.format.directory:
              # Replace the key corresponding to the primary file with '.' to
              # match the way that checksums are created by Arcana
              primary = fileset.format.assort_files(checksums.keys())[0]
              checksums['.'] = checksums.pop(primary)
          return checksums