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Random notes about PyPy

What is the problem with PyPy?

PyPy is fast, much faster than CPython, but it's still not widely used by users. What is the problem? Or what are the problems?

  • Bad support of the :ref:`Python C API <c-api>`: PyPy was written from scratch and uses different memory structures for objects. The cpyext module emulates the Python C API but it's slow.
  • New features are first developped in CPython. In january 2016, PyPy only supports Python 2.7 and 3.2, whereas CPython is at the version 3.5. It's hard to have a single code base for Python 2.7 and 3.2, Python 3.3 reintroduced u'...' syntax for example.
  • Not all modules are compatible with PyPy: see PyPy Compatibility Wiki. For example, numpy is not compatible with PyPy, but there is a project under development: pypy/numy. PyGTK, PyQt, PySide and wxPython libraries are not compatible with PyPy; these libraries heavily depend on the Python C API. GUI applications (ex: gajim, meld) using these libraries don't work on PyPy :-( Hopefully, a lot of popular modules are compatible with PyPy (ex: Django, Twisted).
  • PyPy is slower than CPython on some use cases. Django: "PyPy runs the templating engine faster than CPython, but so far DB access is slower for some drivers." (source of the quote)

If I understood correctly, Pyjston will have same problems than PyPy since it doesn't support the Python C API neither. Same issue for Pyjion?

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