[pywin32-bugs] [ pywin32-Bugs-3521993 ] pythoncom returns wrong object type

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Bugs item #3521993, was opened at 2012-04-27 05:52
Message generated for change (Tracker Item Submitted) made by daveblob
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Category: com
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Dave Blob (daveblob)
Assigned to: Nobody/Anonymous (nobody)
Summary: pythoncom returns wrong object type

Initial Comment:
I’m trying to instantiate a 3rd party com object (Bloomberg’s blpapicom2.Session.1), which works fine via:

	win32com.client.Dispatch (‘blpapicom2.Session.1’)

Except for the fact that it returns the interface of another class (IProviderSession instead of ISession).  Instantiating the COM object in excel is not problematic - it returns an object with the correct interface.  

I’ve traced through the C++ code of pywincom, and nothing unusual seems to be happening – I get the right CLSID back from PyWinObject_AsIID (I get {CLSID_Session Class});  When GetTypeInfo and GetTypeAttr are called I get the wrong interface (IProviderSession).  

Aware that there might be a problem with Bloomberg's COM dll, I wrote my own test in C++ which, I think, makes the calls in the same order as win32com.client.Dispatch:

#include "stdafx.h"
#include <Objbase.h>

int _tmain(int argc, _TCHAR* argv[])
{
	CLSID clsid;
	CLSID iid = IID_IUnknown;

	IUnknown *punk = NULL;
	IDispatch *result = NULL;
	ITypeInfo *pti = NULL;

	TYPEATTR *attr;

	DWORD dwClsContext = CLSCTX_SERVER;

	CoInitialize(NULL);

	LPOLESTR clsName = OLESTR("blpapicom2.Session.1");
	HRESULT hr = CLSIDFromString(clsName, &clsid);
	SCODE sc = CoCreateInstance(clsid, punk, dwClsContext, iid, (void **)&result);

	SCODE sc2 = ((IDispatch *)result)->GetTypeInfo(0, LOCALE_USER_DEFAULT, &pti);

	pti->GetTypeAttr(&attr);

	return 0;
}

Run from the debugger, attr contains IID_ISession at the end of the program.  Inside my Python script PyITypeInfo::GetTypeAttr attr contains IProviderSession.  Fearful that something could be happening between python calls, I modified pythoncom_CoCreateInstance to contain:

	/* BLOB */
	ITypeInfo *pti = NULL;
	SCODE sc2 = ((IDispatch *)result)->GetTypeInfo(0, LOCALE_USER_DEFAULT, &pti);

	TYPEATTR *attr;
	pti->GetTypeAttr(&attr);

before the final return and attr still incorrectly contains IID_IProviderSession.

I've tried this with my current version of Python (2.6.4), a newer one (2.6.8) as well the current release (2.7.3);  All are 32bit versions.  I'm using Windows 7 64bit.  I think all versions as well as my test case were compiled with the 6.0A version of the windows SDK (though I do have 7.0 installed as well).  I have an old windows XP machine and it exhibits the same problem (it is running Python 2.6.2), so I don’t think this is a 32/64 bit problem.

Instantiating by GUID has the same problem.

As an aside, I downloaded OLEViewer and that the Session class is implemented as dual - could this be affecting things?   Even so, I'm still confused as to why Excel and my sample code work and pythoncom does not...

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