pypy is generally incompatible with CPython libraries -- most notable being plain vanilla numpy. There are ongoing attempts to port numpy to pypy (numpypy), but

pypy is generally incompatible with CPython libraries -- most notable being plain vanilla numpy. There are ongoing attempts to port numpy to pypy (numpypy), but other than that you're just left with pure python and pure python libraries. Numba/Cython restrict what kind of code you can write so they can (jit-)compile it. Cython is less restrictive since it's more mature but it uses special syntax and is technically not python anymore.