It's because PyPy relies on traced runtime statistics for optimizations via inlining. There's another approach where you translate your typed program into a low

It's because PyPy relies on traced runtime statistics for optimizations via inlining. There's another approach where you translate your typed program into a lower-level target language and compile it into a native binary. See https://github.com/mypyc/mypyc https://github.com/mypyc/mypyc and https://github.com/cython/cython/wiki/Python-Typing-Proposal https://github.com/cython/cython/wiki/Python-Typing-Proposal