[Distutils] Windows Python sys.prefix

Ian Bicking ianb at colorstudy.com
Wed Sep 19 00:51:57 CEST 2007

Mark Hammond wrote:
>> How does Python on Windows determine sys.prefix?
> By consulting the registry.  The main use-case for that is when Python is
> embedded in another executable - often, but not always, via COM.  When
> Python is hosted inside excel.exe, for example, its impossible to calculate
> sys.path or sys.prefix based on that executable.  In that same example,
> Python's DLL will have been loaded from a directory on the global PATH,
> which generally means the \Windows\System32 directory - so that too is no
> help in calculating the path.
> [IIRC, Python actually tries to use the executable to locate its 'landmark'
> and only falls back to the registry when that fails - but that sounds
> exactly like what is happening in your example.  The gory details are in
> PC/getpathp.c]

I can certainly create a landmark if at all reasonable.  I'm looking at 
getpathp.c, and it looks like it just looks for lib/os.py ... and I 
think it walks up from the current directory until it finds it?  So 
right now I have:


But perhaps if I just change it to:


it will work?  On windows, does it just leave out the "/python2.5/" 
portion of the lib path?

>> Is there a way to effect that?
> Setting PYTHONHOME in the environment is the only way I'm aware of.

That's kind of what workingenv did, which I'm trying to avoid -- you 
have to worry about, for instance, calling another Python subprocess if 
you don't want that process to be in the same environment.

Ian Bicking : ianb at colorstudy.com : http://blog.ianbicking.org
             : Write code, do good : http://topp.openplans.org/careers

More information about the Distutils-SIG mailing list