pythoncom.CoCreateInstance always fail

[AndrewChan2022]

• Expected behavior and actual behavior.

create SetupConfigurationClass success, but fail

• Steps to reproduce the problem.

step 1. install visual studio on the windows, so there are com class SetupConfigurationClass

document here Microsoft.VisualStudio.Setup.Configuration

step 2. create com object of SetupConfigurationClass fail

import pythoncom, pywintypes

pythoncom.CoInitialize()

clsid = pywintypes.IID("{177F0C4A-1CD3-4DE7-A32C-71DBBB9FA36D}")
iid = pywintypes.IID("{42843719-DB4C-46C2-8E7C-64F1816EFD5B}")
obj = pythoncom.CoCreateInstance(clsid, None, 1, iid)
print(obj)

step 3. however using raw ctypes method success

import ctypes
from ctypes import *

class GUID(Structure):
    _fields_ = [("Data1", c_ulong),
                ("Data2", c_ushort),
                ("Data3", c_ushort),
                ("Data4", c_ubyte * 8)]

### init
ole32 = WinDLL('Ole32.dll')
CoInitialize = ole32.CoInitialize
CoUninitialize = ole32.CoUninitialize
CoCreateInstance = ole32.CoCreateInstance

rc = CoInitialize(None)

### create instance
clsid = GUID(0x177F0C4A, 0x1CD3, 0x4DE7,
        (0xA3, 0x2C, 0x71, 0xDB, 0xBB, 0x9F, 0xA3, 0x6D ))
iid = GUID(0x42843719, 0xDB4C, 0x46C2,
        (0x8E, 0x7C, 0x64, 0xF1, 0x81, 0x6E, 0xFD, 0x5B))
clsctx = 1
obj = c_void_p(None)
rc = CoCreateInstance(byref(clsid), 0, clsctx, byref(iid), byref(obj))
print(rc)
print(obj)

• Version of Python and pywin32

Name: pywin32 Version: 306

Python 3.11.4

[mhammond]

This is almost certainly because the interface in question doesn't support IDispatch

[AndrewChan2022]

No, this component is used by customer to query visual studio version info, so no need support IDispatch and ole features.

As my understand, pythoncom is by design to support only subset of com that support IDispatch interface, so I need use other approach to get this non-ole component?

[AndrewChan2022]

I using ctypes to accomplish this task.

I think COM without IDispatch maybe apply to lightweight tasks like finding VisualStudio installation.

https://github.com/AndrewChan2022/PyVisualStudioSetupConfiguration

[mhammond]

In that case I think you could have just use IID_IUnknown - but it sounds like there's nothing to do here.

[AndrewChan2022]

yes, pythoncom also success when I change the iid to IUnknown, but still cannot query other interface by IUnknown :)

thanks.

import pythoncom, pywintypes

pythoncom.CoInitialize()

clsid = pywintypes.IID("{177F0C4A-1CD3-4DE7-A32C-71DBBB9FA36D}")
iid = pywintypes.IID("{00000000-0000-0000-C000-000000000046}")
obj = pythoncom.CoCreateInstance(clsid, None, 1, iid)
print(obj)

output:

<PyIUnknown at 0x000001DD5FEA20A0 with obj at 0x000001DD5FEA2190>