def _iter_filename_over_mountpoints(self, filename):
    '''iterate absolute filename over self.mountpoints and self.root'''
    for mountpoint in self.mountpoints + [self.root]:
        _drivename, _filename = os.path.splitdrive(filename)
        _filename = _filename.lstrip(os.path.sep)
        yield os.path.join(_drivename + mountpoint, _filename)