Imagine changing core features of your codebase and then the compiler / type checker telling you all the places that you needed to fix it. Then when it's fixed,

Imagine changing core features of your codebase and then the compiler / type checker telling you all the places that you needed to fix it. Then when it's fixed, the code runs flawlessly. That's happened a LOT in my 10 years of C++ development. I can leverage the compiler to do 90% of the refactoring work. For example, say you want to remove a field from an object in C++. The compiler will tell you every place where the field is accessed and raise a compiler error. In python this won't manifest until the code is run in that particular spot. I can only imagine that in this type of language a well intentioned refactor could easily create 10 bugs that don't get triggered for a very long time.