"Manually handling headers"? That is how people wrote websites in the early 2000s. Many cgi scripts were cobbled together in Perl. I found that I liked Python better.

I understand that in PHP you just add some <?php ...> stuff to an otherwise normal HTML file, but the situation in Python, with its multiline strings that support variable interpolation, isn't much worse. Just add the lines I mentioned to the top (treat is as a recipe if you like), and the rest is better than PHP.