streams.py 文件源码

def seek(self, offset, whence=io.SEEK_SET):
        # Recalculate offset as an absolute file position.
        if whence == io.SEEK_SET:
            pass
        elif whence == io.SEEK_CUR:
            offset += self._pos
        elif whence == io.SEEK_END:
            if self._size < 0:
                # Finish reading the file
                while self.read(io.DEFAULT_BUFFER_SIZE):
                    pass
            offset += self._size
        else:
            raise ValueError('Invalid value for whence: {}'.format(whence))

        if offset < 0:
            msg = '[Error {code}] {msg}'
            raise IOError(msg.format(code=errno.EINVAL,
                                     msg=os.strerror(errno.EINVAL)))

        # Make it so that offset is the number of bytes to skip forward.
        if offset < self._pos:
            self._rewind()
        else:
            offset -= self._pos

        # Read and discard data until we reach the desired position
        while offset > 0:
            data = self.read(min(io.DEFAULT_BUFFER_SIZE, offset))
            if not data:
                break
            offset -= len(data)

        return self._pos