code: def _get_interval(variant_regions, region, out_file, items):
      
      target = shared.subset_variant_regions(variant_regions, region, out_file, items)
      if target:
          if isinstance(target, six.string_types) and os.path.isfile(target):
              return "--interval %s" % target
          else:
              return "--interval %s" % bamprep.region_to_gatk(target)
      else:
          return ""
docs: Retrieve interval to run analysis in. Handles no targets, BED and regions
  
      region can be a single region or list of multiple regions for multicore calling.