'Set the file\'s current position.
Args:
offset: seek offset as number.
whence: seek mode. Supported modes are os.SEEK_SET (absolute seek),
and os.SEEK_CUR (seek relative to the current position) and os.SEEK_END
(seek relative to the end, offset should be negative).'

def seek(self, offset, whence=os.SEEK_SET):

    self._verify_read_mode()
    if (whence == os.SEEK_SET):
        self._offset = offset
    elif (whence == os.SEEK_CUR):
        self._offset += offset
    elif (whence == os.SEEK_END):
        file_stat = self.stat()
        self._offset = (file_stat.st_size + offset)
    else:
        raise InvalidArgumentError('Whence    mode    %d    is    not    supported', whence)
