It seems changing os.environ['PATH'] is a security risk and is not allowed for Windows Store apps. The suggestion in the NumPy issue is to:

- use AddDllDirectory, (which is as accessable as os.environ['PATH'] but is not considered a security risk so far), but this requires using SetDefaultDllDirectories which breaks other things

- put any dlls required for the c-extension pyd in the same directory which means scipy and numpy will be using duplicate and potentially different OpenBLAS dlls, and whoever imports first wins

- load all the required dlls via LoadLibrary, meaning NumPy will have to export a windows-only API to SciPy so the latter can know where the DLL is.

I am glad NumPy only has one DLL, and not a dozen like QT or wxPython. 

Is there a PEP that describes the overall design of windows directory layout or a design guide for package authors with best practices for additional dll dependencies?