def _contentRange(self, offset, size):
        """
        Return a string suitable for the value of a Content-Range header for a
        range with the given offset and size.

        The offset and size are not sanity checked in any way.

        @param offset: How far into this resource the range begins.
        @param size: How long the range is.
        @return: The value as appropriate for the value of a Content-Range
            header.
        """
        return networkString('bytes %d-%d/%d' % (
            offset, offset + size - 1, self.getFileSize()))

        Return a string suitable for the value of a Content-Range header for a
        range with the given offset and size.

        The offset and size are not sanity checked in any way.

        @param offset: How far into this resource the range begins.
        @param size: How long the range is.
        @return: The value as appropriate for the value of a Content-Range
            header.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/static.py