Python is a convenient friendly syntax for calling code implemented in C. While you can easily re-implement the syntax, you then have to decide how much of that C to re-implement. A few of the builtin types are easy (eg strings and lists), but it soon becomes a mountain of code and interoperability, especially if you want to get the semantics exactly right. And that is just the beginning - a lot of the value of Python is in the extensions, and many popular ones (eg numpy, sqlite3) are implemented in C and need to interoperate with your re-implementation. Trying to bridge from Java or .NET to those extensions will overwhelm any performance advantages you got.
This JIT approach is improving the performance of bits of the interpreter while maintaining 100% compatibility with the rest of the C code base, its object model, and all the extensions.
This JIT approach is improving the performance of bits of the interpreter while maintaining 100% compatibility with the rest of the C code base, its object model, and all the extensions.