code: def write_quota(outbytes: int, outfn: Path) -> Union[None, int]:
      
      if not outfn:
          return None
  
      anch = Path(outfn).resolve().anchor
      freeout = shutil.disk_usage(anch).free
  
      if freeout < 10 * outbytes:
          raise IOError(f'out of disk space on {anch}.'
                        '{freeout/1e9} GB free, wanting to write {outbytes/1e9} GB.')
  
      return freeout
docs: aborts writing if not enough space on drive to write