code: def _Open(self, path_spec=None, mode='rb'):
      
      if not path_spec:
        raise ValueError('Missing path specification.')
  
      if not path_spec.HasParent():
        raise errors.PathSpecError(
            'Unsupported path specification without parent.')
  
      self._gzip_file_object = resolver.Resolver.OpenFileObject(
          path_spec.parent, resolver_context=self._resolver_context)
      file_size = self._gzip_file_object.get_size()
  
      self._gzip_file_object.seek(0, os.SEEK_SET)
  
      uncompressed_data_offset = 0
      next_member_offset = 0
  
      while next_member_offset < file_size:
        member = gzipfile.GzipMember(
            self._gzip_file_object, next_member_offset, uncompressed_data_offset)
        uncompressed_data_offset = (
            uncompressed_data_offset + member.uncompressed_data_size)
        self._members_by_end_offset[uncompressed_data_offset] = member
        self.uncompressed_data_size += member.uncompressed_data_size
        next_member_offset = member.member_end_offset
docs: Opens the file-like object defined by path specification.
  
      Args:
        path_spec (Optional[PathSpec]): path specification.
        mode (Optional[str]): file access mode.
  
      Raises:
        AccessError: if the access to open the file was denied.
        IOError: if the file-like object could not be opened.
        OSError: if the file-like object could not be opened.
        PathSpecError: if the path specification is incorrect.
        ValueError: if the path specification is invalid.