docs: def extractfile(self, member):
          '''
          Extract a member from the archive as a file object. `member' may be
          a filename or an RPMInfo object.
          The file-like object is read-only and provides the following
          methods: read(), readline(), readlines(), seek() and tell()
          '''
          if not isinstance(member, RPMInfo):
              member = self.getmember(member)
          return _SubFile(self.data_file, member.file_start, member.size)