Final report: ctypes and NumPy work with JyNI on Windows
After the last report, where I managed to run DemoExtension with JyNI on Windows, I investigated workability of ctypes. Linking msvcrt The first thing I discovered was that it didn't work: Exception in thread "main" java.lang.UnsatisfiedLinkError: D:\workspace\linux\JyNI\build\JyNI.dll\python27.dll: Can't find dependent libraries And further – that DemoExtension also was not working when built using setup.py rather than by my makefile . That was a drawback, but remember that DemoExtension was working fine with CPython, even if built with the makefile. After carefully studying the difference between the build commands I found out that setup.py would add the /MD flag . Beneath several other options, e.g. /nologo /Ox /W3 /GS- /DNDEBUG, /MD was the one that made the difference. It tells MSVC to link msvcrt.dll , precisely speaking msvcr90.dll for Python 2.7. I guess the DemoExtension build without explicit /MD worked, because it still linked libcmt.lib. However