There is an old project for parametric svg here: https://github.com/parametric-svg/

That project is not maintained anymore and it is almost dead. But the general idea is very attractive and useful, so I have developed an Inkscape extension to support this kind of parametric stuff here:

The main differences with the mentioned previous project is that this is actually an Inkscape extension, it works directly inside inkscape and the scripting language is plain old python.

I hope you can find it useful, any comments and suggestions are welcome.
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