<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def extra_info(self):
 """Retrieve the log string generated when opening the file."""

        info = _ffi.new("char[]", 2**14)
        _snd.sf_command(self._file, _snd.SFC_GET_LOG_INFO,
                        info, _ffi.sizeof(info))
        return _ffi.string(info).decode('utf-8', 'replace')