PyPy — How can it possibly beat CPython?

Question

From the Google Open Source Blog:

PyPy is a reimplementation of Python in Python, using advanced techniques to try to attain better performance

Answer 1

PyPy is implemented in Python, but it implements a JIT compiler to generate native code on the fly.

The reason to implement PyPy on top of Python is probably that it is simply a very productive language, especially since the JIT compiler makes the host language's performance somewhat irrelevant.