[pywin32-bugs] [ pywin32-Bugs-2174265 ] return object from method fails

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Bugs item #2174265, was opened at 2008-10-17 01:58
Message generated for change (Comment added) made by mhammond
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Category: com
Group: None
>Status: Closed
>Resolution: Invalid
Priority: 5
Private: No
Submitted By: Enrico (enrico-b)
Assigned to: Nobody/Anonymous (nobody)
Summary: return object from method fails

Initial Comment:
From pippo.idl (in test directory)
HRESULT Method1([out, retval] IPippo **val)

When called from C++ there's an exception

I attach a client written with python and comtypes and, with a little effort I
can see the problem is a call to QueryInterface with IID_NULL (as happens if the caller
is a C++ client).

client: pippo-test.py

To show the problem I registered the pippo_server with the --debug option.
Then I changed the function Method1 in this way to have a debug output:

    def Method1(self):
        #return wrap(CPippo())
        return wrap(CPippo(),useDispatcher=1)

Last, in the file policy.py at line 261, at the begin of the
_QueryInterface_ function I added a line:
    print iid

The result in PythonWin trace Collector is:

Object with win32trace dispatcher created (object=None)
Object with win32trace dispatcher created (object=<pippo_server.CPippo
instance at 0x015DF210>)
{00000000-0000-0000-0000-000000000000}Traceback (most recent call last):
  File "C:Python25Libsite-packageswin32comserverdispatcher.py", line 41, in
_QueryInterface_
    return self.policy._QueryInterface_(iid)
  File "C:Python25libsite-packageswin32comserverpolicy.py", line 261, in
_QueryInterface_
    print iid
com_error: (-2147221005, "Stringa dell'interfaccia non valida.", None, None)
pythoncom error: Failed to call the universal dispatcher


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>Comment By: Mark Hammond (mhammond)
Date: 2012-01-27 21:23

Message:
I think this is a problem in the caller - I don't think there is a
requirement for objects to return something when queried with IID_NULL.

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