[fastball]

The problem with PyPy is that it doesn't support the C-API, which is required for all those other high performance libraries.

So you gain the perf of a JIT, while losing out on most everything else high-performance in the Python ecosystem.

[masklinn]

Pypy has cpyext which implements a subset of the C-API, however it comes with a long list of caveats, and is more of a backstop, they very much prefer cffi.