The concept of a distribution ('distro') is that it is a collection of programs, OS components, configurations, and installer distributed as a complete package, and often including many components that are only downloaded on demand. Very little of each distro is actually written by the vendor or packager, and the bulk of the distro is written in whatever language(s) is deemed appropriate by the original authors.
In most cases, the programming language used to create a program is invisible, or nearly so, and only very rarely is there any intent to expose the implementation language. If the language is compiled, one usually has to do some work to get and see the source code. So this begs the question of why you would want a distro written in Python (or any other language for that matter). If it is for the purpose of academic interest and study of code, I think you can find a substantial list of applications with
Applications Written in Python as a jumping off point.
Or, is there something about a distro in particular that you want to dissect? If so, please elaborate.
--- rod.