[python-win32] pythoncom.CoCreateInstance(...) problems

[Pete Hodgson]

Hi all,

Firstly, apologies for any dumbness, I'm a python newbie.

I'm trying to use pythoncom to build a DirectShow Filter Graph, but I'm 
having problems getting the correct COM interface with 
pythoncom.CoCreateInstance(...). To try and diagnose the problem, I've 
written a toy C program which seems to me to be directly equivalent to 
the python script I'm having problems with. Here are the two programs:

<------------START OF MY PYTHON IMPLEMENTATION--------------------->

import pythoncom

CLSID_FilterGraph = 
pythoncom.MakeIID('{E436EBB3-524F-11CE-9F53-0020AF0BA770}')
IID_IGraphBuilder = 
pythoncom.MakeIID('{56A868A9-0AD4-11CE-B03A-0020AF0BA770}')

print "CLSID_FilterGraph:", CLSID_FilterGraph
print "IID_IGraphBuilder:", IID_IGraphBuilder

pythoncom.CoInitialize()

IFilterGraph = pythoncom.CoCreateInstance( CLSID_FilterGraph, None, 
pythoncom.CLSCTX_INPROC_SERVER, IID_IGraphBuilder )

<------------END OF MY PYTHON IMPLEMENTATION--------------------->

When I run the above from IDLE, I get the following:

<----------PYTHON OUTPUT--------------->
IDLE 1.0.3      ==== No Subprocess ====
 >>>
CLSID_FilterGraph: {E436EBB3-524F-11CE-9F53-0020AF0BA770}
IID_IGraphBuilder: {56A868A9-0AD4-11CE-B03A-0020AF0BA770}
Traceback (most recent call last):
   File "D:\work\Personal\RM2MP3\rm2mp3.py", line 11, in ?
     IFilterGraph = pythoncom.CoCreateInstance( CLSID_FilterGraph, None, 
pythoncom.CLSCTX_INPROC_SERVER, IID_IGraphBuilder )
TypeError: There is no interface object registered that supports this IID
 >>>
<------END PYTHON OUTPUT--------------->


<------------START OF MY C IMPLEMENTATION--------------------->

#include "stdafx.h"
#include "dshow.h"


int _tmain(int argc, _TCHAR* argv[])
{
	HRESULT hr;

	if( FAILED( CoInitialize(NULL) ) )
		return -1;

	GUID _CLSID_FilterGraph;
	UuidFromString(
		(unsigned char*)"E436EBB3-524F-11CE-9F53-0020AF0BA770"
		, &_CLSID_FilterGraph );

	GUID _IID_IGraphBuilder;
	UuidFromString(
		(unsigned char*)"56A868A9-0AD4-11CE-B03A-0020AF0BA770"
		, &_IID_IGraphBuilder );

	IGraphBuilder *pIGraphBuilder;
	hr = CoCreateInstance(
		_CLSID_FilterGraph, NULL
		, CLSCTX_INPROC_SERVER, IID_IGraphBuilder
		, (void**) &pIGraphBuilder );
	if( FAILED(hr) )
		return -2;

	return 0;
}

<------------END OF MY C IMPLEMENTATION--------------------->

The above C implementation compiles and runs fine, returning 
"CoCreateInstance(...) succeeded".

Can anyone see why the C implementation works and the python one 
doesn't? I'm using the same CLSIDs and IIDs for both, and calling 
CoCreateInstance(...) in an identical manner. Any suggestions gratefully 
received!

Cheers,

Pete