def write(pkg_file, pkg_rels, parts):
        """
        Write a physical package (.pptx file) to *pkg_file* containing
        *pkg_rels* and *parts* and a content types stream based on the
        content types of the parts.
        """
        phys_writer = PhysPkgWriter(pkg_file)
        PackageWriter._write_content_types_stream(phys_writer, parts)
        PackageWriter._write_pkg_rels(phys_writer, pkg_rels)
        PackageWriter._write_parts(phys_writer, parts)
        phys_writer.close()