streams.py 文件源码

def seek(self, offset, whence=io.SEEK_SET):
        """
        Change the stream position to the given byte *offset*. *offset* is
        interpreted relative to the position indicated by *whence*. Values for
        *whence* are:

        * ``SEEK_SET`` or ``0`` – start of the stream (the default); *offset*
          should be zero or positive

        * ``SEEK_CUR`` or ``1`` – current stream position; *offset* may be
          negative

        * ``SEEK_END`` or ``2`` – end of the stream; *offset* is usually
          negative

        Return the new absolute position.
        """
        with self.lock:
            if whence == io.SEEK_CUR:
                offset = self._pos + offset
            elif whence == io.SEEK_END:
                offset = self._length + offset
            if offset < 0:
                raise ValueError(
                    'New position is before the start of the stream')
            self._set_pos(offset)
            return self._pos