sys.prefix in COM

[Gordon McMillan]

Sue Giller wrote:

[...]
> I have finally looked into this, and I wonder if there might be a 
> problem in sys.prefix in COM.  I am a python wannabe, so I am not 
> sure if the following is expected or what.
> 
> I created a simple COM object in python that returns the state of 
> sys.prefix, and sys.path. 

[...]

> If I run a test case in python that makes the COM object using 
> win32com.server.dispatch, it nicely prints out a good sys.prefix and 
> a path.

[...]

> However, if I create the COM object in VB6, I get a blank string back 
> for sys.prefix.


> Prefix: :
> C:\Python21\scripts\com
> etc.....
> 
> With the blank prefix, the path has dropped any items that are 
> located via *.pth files in my base python directory, thus loosing 
> things like Numeric that is installed in my c:\python21 directory.

Excellent detective work.
 
> I am unsure what exactly sys.prefix should be pointing to (I am 
> assuming it is where my python 'stuff' is installed to; c:\python21 in 
> my case), but I can't believe the string should be blank.
> 
> Does anyone have any insights into this?  I don't want to have to 
> hardwire my base python directory into my various com objects to 
> get them to find these other libraries, etc.  I have done that up to 
> now, but I need to make these objects more general so they will 
> work on any python site.

There is a reason for this. sys.prefix is really only meaningful on *nix. On  
Windows it is usually taken (correctly) to mean "where the executable is". 
site.py & friends can be picked up from there.

If you registered your COM objects as CLSCTX_LOCAL_SERVER you would indeed 
have a sys.prefix. But if it's inprocess, the executable isn't Python. In 
fact, pythoncomXX.dll loaded pythonXX.dll for you, and without knowing where 
their python.exe lives, they're lost. Well, only a little.

I've never encountered this problem, but I'd guess you could tweak Python's 
registry entries to get around this.

-- Gordon
http://www.mcmillan-inc.com/