questions about a C++ COM object accessed in Python via win32com

[T.T.H.]

Hi

I am coding a C++ COM object which I want to access in Python. For that
I do have some detail questions and need help since I am not that familiar
with the documentation itself of Python and win32com yet.


1.
How do I know that...

import win32com.client

....was successful or not?


2.
In my COM object I do have the following C++ function:

STDMETHODIMP CMyTestObjekt:: Connect()
{
if (m_boolReadyToC onnect == false) {
return E_FAIL;
}
return S_OK;
}

How do I know in Python whether I got back a S_OK or an E_FAIL? Or is this
whole concept wrong and I should better make an additional return value like:

MyFunktion(.... ..., [out, retval] BOOL *pVal); (declaration in the IDL)


3.
If I execute the following command...

MyObject = win32com.client .Dispatch("MyCO M.MySuperCOMObj ect")

....what is the return value from which I know whether it was successful?
Or what can be the ""content"" of "MyObject" afterwards?


4.
If I have a function in Python in which I call the (global) COM Object,
what "if" do I have to use to know whether the COM object already had
been allocated? I tried the following but that didn't work:

def foo():
if MyObject == None:
print "COM not there yet"
else:
print MyObject.Messag e


I'd really appreciate any help. Or even a hint where to look in the "original"
documentation. FYI: I do use Win2000 and ActiveState ActivePython 2.2 which
already includes win32com.

Bye,
Matthias "T.T.H." Grobe

[Alex Martelli]

Re: questions about a C++ COM object accessed in Python via win32com

T.T.H. wrote:
[color=blue]
> Hi
>
> I am coding a C++ COM object which I want to access in Python. For that
> I do have some detail questions and need help since I am not that familiar
> with the documentation itself of Python and win32com yet.
>
>
> 1.
> How do I know that...
>
> import win32com.client
>
> ...was successful or not?[/color]

If it fails, it raises an exception -- so, if you want to handle the
failure, you try this statement in the try clause of a try/except
statement. That is reasonably similar to C++'s exception (syntax
apart), so the concept shouldn't be too alien.

[color=blue]
> 2.
> In my COM object I do have the following C++ function:
>
> STDMETHODIMP CMyTestObjekt:: Connect()
> {
> if (m_boolReadyToC onnect == false) {
> return E_FAIL;
> }
> return S_OK;
> }
>
> How do I know in Python whether I got back a S_OK or an E_FAIL? Or is this[/color]

E_FAIL translates into an exception.
[color=blue]
> whole concept wrong and I should better make an additional return value
> like:
>
> MyFunktion(.... ..., [out, retval] BOOL *pVal); (declaration in the IDL)[/color]

This would be much more COM-idiomatic, unless the failure IS an exceptional
event, something that SHOULD not happen in a well-functioning system and
probably the result of mis-configuration or hardware malfunctioning.
[color=blue]
>
> 3.
> If I execute the following command...
>
> MyObject = win32com.client .Dispatch("MyCO M.MySuperCOMObj ect")
>
> ...what is the return value from which I know whether it was successful?[/color]

Guess...?-) Yep: if it's not successful it raises an exception!
[color=blue]
> Or what can be the ""content"" of "MyObject" afterwards?[/color]

If an exception wasn't raised, MyObject is an instance of some class
(you need not care about which one...) on which you can call methods
(which will be "proxied" to the actual C++-implemented COM object).
[color=blue]
>
> 4.
> If I have a function in Python in which I call the (global) COM Object,
> what "if" do I have to use to know whether the COM object already had
> been allocated? I tried the following but that didn't work:
>
> def foo():
> if MyObject == None:
> print "COM not there yet"
> else:
> print MyObject.Messag e[/color]

If name "MyObject" has never been bound, trying to access it will...
I give you three guesses... *raise an exception*!

However, I _would_ suggest that in this case you set MyObject=None
at a global level and test as above (except, use "Myobject is None"
rather than ==) -- that is more idiomatic in Python.


Alex

[T.T.H.]

Re: questions about a C++ COM object accessed in Python via win32com

> Alex Martelli <aleax@aleax.it >

Praise you, Alex, that was the most precise answer I could have imagined!

Bye,
T.T.H.

[T.T.H.]

Re: questions about a C++ COM object accessed in Python via win32com

> Alex Martelli <aleax@aleax.it >

Praise you, Alex, that was the most precise answer I could have imagined!

Bye,
T.T.H.