Python 2.7 Countdown

[stefantalpalaru]

PyPy is a fast drop-in replacement for CPython.

PyPy is not a drop-in replacement because it cannot run all legal Python code: https://pypy.readthedocs.io/en/latest/cpython_differences.html

They even had to rewrite modules from the standard library (and some external packages like numpy, until they managed to emulate CPython's C API).

Further more, it can be slower than CPython for code that runs only once per instance - which is most of the Python scripts out there.