Comment by BeetleB

As others have said, you are reinventing the Static Site Generator. I would strongly urge you to look into those.

If you know Python well enough, my recommendation is Pelican.[1] You can author your posts in Markdown. You specify the desired HTML/CSS. It will then do all the boring work for you. Then just upload the static files to a webserver.

[1] https://getpelican.com/