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What are the builtin and third-party libraries that people have had trouble with when using PyPy (modulo having to configure an appication to use PyPy at runtime instead of CPython)? For web-dev, scientific or otherwise?

In particular, are there any such problem cases where there is insufficient documentation?

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Cython is the biggest issue right now with PyPy: lots of 3rd party libraries depend on it, lxml and pyzmq come to mind.

I can't wait for Cython support: in our tests PyPy delivers amazing RAM savings, PyPy seems to have a particularly efficient list implementation specialized for small strings: we're seeing x3 savings there, in addition to 20% speedup.

If Cython compiles to standard c modules, and pypy claims to support standard c modules in its latest release, doesn't pypy now support Cython? (In the same way that Cpython does?)

PyPy's support for the C API is highly limited and not something to be relied upon for new code. IIRC the Cython plan is for Cython to grow the ability to emit pure Python with ctypes.

PyPy doesn't have a specialized list for small strings. It might land one in the near future, your findings are a bit weird, but objects might be smaller because of smaller GC headers.

Cheers, fijal

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