[python-win32] Accessing other interfaces of a Dispatch created COM object

[Mark Hammond]

Look at the docstring for win32com.client.CastTo (and googling for that will
probably help too)

Cheers,

Mark

> I just discovered a third possibility, and subsequent failure:
> 
> >>> obj_i2 = Dispatch(obj, None, Interface_2.CLSID)
> >>> obj_i2.secondaryMethod()
> Traceback (most recent call last):
> ...
>   File "C:\Python25\lib\site-packages\win32com\client\__init__.py",
> line 449, in _ApplyTypes_
>     dispid, 0, wFlags, retType, argTypes, *args),
> com_error: (-2147352573, 'Member not found.', None, None)
> 
> Alec
> 
> On Thu, Aug 28, 2008 at 10:33 AM, Alec Munro <alecmunro at gmail.com>
> wrote:
> > Oh, and on re-reading, I do realize that the DLL itself doesn't
> > implement those interfaces. There's a class within the DLL that does
> > that. :)
> >
> > On Thu, Aug 28, 2008 at 10:32 AM, Alec Munro <alecmunro at gmail.com>
> wrote:
> >> Hi List,
> >>
> >> Hopefully I have my terminology right, I'm pretty new to COM and
> C++.
> >>
> >> My problem is that I have a COM DLL written in C++, that I would
> like
> >> to call from Python. This DLL implements 3 important interfaces,
> each
> >> of which is also an IDispatch implementation, like the following:
> >>
> >> IDispatchImpl<Interface_1, &__uuidof(Interface_1),
> &LIBID_Interface_1, 1, 0>
> >> IDispatchImpl<Interface_2, &__uuidof(Interface_2),
> &LIBID_Interface_2, 1, 0>
> >> IDispatchImpl<Interface_3, &__uuidof(Interface_3),
> &LIBID_Interface_3 1, 0>
> >>
> >>  However, when I do:
> >>>>> obj = win32com.client.Dispatch("a.b.c")
> >>>>> obj
> >> <COMObject a.b.c>
> >>
> >> The object I get only has methods available for the first of the
> >> interfaces. From my reading, this is simply the functionality of
> >> IDispatch, and if I wanted to get those additional methods through
> >> IDispatch, I would have to update the DLL, and restructure my
> >> interfaces. I'm not confident enough in my C++ to do this, or at
> least
> >> it's not my first choice.
> >>
> >> From what I've read, there are two ways that seem to be
> possibilities
> >> for being able to call the methods from the other interfaces.
> >>
> >> The simplest one I found was the suggestion to use MakePy on the
> type
> >> library containing Interface_2 and Interface_3. I did this, and
> copied
> >> the generated file to my working directory, then did:
> >>
> >>>>> from interfaces import Interface_2
> >>>>> obj_i2 = Interface_2(obj)
> >>>>> obj_i2
> >> <win32com.gen_py.typelibname 1.0 Type Library.Interface_2 instance
> at
> >> 0x17459602>
> >>
> >> Unfortunately when I try:
> >>
> >>>>> obj_i2.secondaryMethod()
> >> Traceback (most recent call last):
> >> ...
> >>  File "C:\Python25\lib\site-packages\win32com\client\__init__.py",
> >> line 449, in _ApplyTypes_
> >>   dispid, 0, wFlags, retType, argTypes, *args),
> >> com_error: (-2147319779, 'Library not registered.', None, None)
> >>
> >> The other suggestion I came across was to use QueryInterface. I
> wasn't
> >> sure what argument to pass to QueryInterface, so I tried using the
> >> CLSID of the interface I wanted.
> >>
> >>>>> obj._oleobj_.QueryInterface(Interface_2.CLSID)
> >> Traceback (most recent call last):
> >>  File "<interactive input>", line 1, in <module>
> >> TypeError: There is no interface object registered that supports
> this IID
> >>
> >> From these error messages, it seems like perhaps there's a problem
> >> with the registration of the type library that contains the
> >> interfaces. I'm not really sure how to fix that, or if that is even
> >> the problem.
> >>
> >> Any ideas?
> >>
> >> Thanks,
> >> Alec Munro
> >>
> >
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