[jmull]

I'm just never going to understand why you'd want to write your HTML in something unlike HTML (Python in this case). Then you need to know the thing that isn't like HTML, plus HTML, plus the details of how the other thing is transformed to HTML.

Of course, we often need something dynamic, so we can't just use HTML. But why not something a lot like HTML so those additional pieces are as small and simple as possible... you know... like a template engine.

[bsima]

Templating engines start out with just variable substitution, but inevitably you want to build logic into your HTML, so it adds if/else statements, then before you know it you are embedding your 'real' programming language into the HTML template itself. Think ERB templates with arbitrary ruby code inside them.

It's more robust to go the other way: start with the full-powered programming language, and emit the static HTML data after doing the complex logic stuff.

[PurpleRamen]

Because HTML is not a programming language, but you do have problems which demand a programming language, and this "something" is the programming language you know. HTML is just a mean to reach their goal. People are usually not writing json or xml by hand either.