def _find_modes(self):
        """Determine the appropriate modes for files and directories."""
        try:
            st = self._transport.stat('.')
        except errors.TransportNotPossible:
            self._dir_mode = 0755
            self._file_mode = 0644
        else:
            self._dir_mode = st.st_mode & 07777
            # Remove the sticky and execute bits for files
            self._file_mode = self._dir_mode & ~07111
        if not self._set_dir_mode:
            self._dir_mode = None
        if not self._set_file_mode:
            self._file_mode = None