Python, comtypes and ArcObjects: Error creating AppROT object

Question

I am experimenting with comtypes and ArcObjects under Python 2.6.5 and ArcGIS 10 SP1. I'm using the pure Python method to wrap the ArcObjects OLBs described in this answer, but getting an error in the comtypes.CoCreateInstance method.

Here is the code I am running:

def WrapModules():
    #force wrapping of all ArcObjects libraries (OLBs)
    import os
    import comtypes.client
    # change com_dir to whatever it is for you
    com_dir = r'C:\Program Files\ArcGIS\Desktop10.0\com'
    coms = [os.path.join(com_dir, x) for x in os.listdir(com_dir) if os.path.splitext(x)[1].upper() == '.OLB']
    map(comtypes.client.GetModule, coms)

def GetApp():
    """Get a hook into the current session of ArcMap"""
    from comtypes.gen import esriFramework
    pAppROT = NewObj(esriFramework.AppROT, esriFramework.IAppROT)
    if pAppROT is not None:
        iCount = pAppROT.Count
        if iCount == 0:
            print 'No ArcGIS application currently running.  Terminating ...'
            return None
        for i in range(iCount):
            pApp = pAppROT.Item(i)  #returns IApplication on AppRef
            if pApp.Name == 'ArcMap':
                print "ArcMap found"
                return pApp
        print 'No ArcMap session is running at this time.'
    print "No AppROT found"
    return None

def NewObj(MyClass, MyInterface):
    """Creates a new comtypes POINTER object where\n\
    MyClass is the class to be instantiated,\n\
    MyInterface is the interface to be assigned"""
    from comtypes.client import CreateObject
    import traceback
    try:
        ptr = CreateObject(MyClass, interface=MyInterface)
        return ptr
    except:
        print traceback.format_exc()
        return None

if __name__ == "__main__":
    WrapModules()
    pApp = GetApp()
    if pApp is not None:
        print "HWND: %d" % pApp.hWnd
    else:
        print "No ArcGIS application found!"

And here is the output from the script:

Traceback (most recent call last):
  File "C:\temp\ComHelpers.py", line 35, in NewObj
    ptr = CreateObject(MyClass, interface=MyInterface)
  File "C:\Python26\ArcGIS10.0\lib\site-packages\comtypes\client\__init__.py", line 235, in CreateObject
    obj = comtypes.CoCreateInstance(clsid, clsctx=clsctx, interface=interface)
  File "C:\Python26\ArcGIS10.0\lib\site-packages\comtypes\__init__.py", line 1145, in CoCreateInstance
    _ole32.CoCreateInstance(byref(clsid), punkouter, clsctx, byref(iid), byref(p))
  File "_ctypes/callproc.c", line 925, in GetResult
WindowsError: [Error -2147221231] ClassFactory cannot supply requested class

No AppROT found
No ArcGIS application found!

Thanks for any insights you might have!

Answer 1

For completeness, this solution was posted by Jason Scheirer over on the GIS Stack Exchange:

Import arcpy first, you aren't doing any license checkout or setting up the ArcObjects 10.0 runtime as-is so it won't find the CoClass.