That's true of most compiled languages. Unless we are talking about asserts, reflection, I think type erasure, and maybe a few other concepts, language runtimes don't check types. C does not check types at runtime. You compile it and then rely on control of invariants and data flow to keep everything on rails. In python, this is tricky because everything is behind at least one layer of indirection, and thus virtually everything is mutable, so it's hard to enforce total control of all data structures. But you can get really close with modern tooling.