And then you get to google scale and realize using python for every config, like your entire build system, leads to a huge mess of completely non-deterministic

And then you get to google scale and realize using python for every config, like your entire build system, leads to a huge mess of completely non-deterministic build scripts that do wacky things like make HTTP calls to prod systems, depend on all kinds of global state stores, etc. So you build a new version of python that strips out all of the non-determinism and move your config to that (see starlark: https://docs.bazel.build/versions/master/skylark/language.html https://docs.bazel.build/versions/master/skylark/language.ht... ).