[python-win32] win32com creates unwanted reference to what is already a pointer

[Simon van Bezooijen]

Hello and good day,

I am having trouble with calling a certain COM interface, (a closed-source 32-bit COM interface DLL of a Robot controller) from my Python application.
Because so far my entire application is made in Python, it would be a nice bonus if I could call this interface directly from Python too. The win32com library seemed perfect for this task.

One of the functions in this interface is the following:
BOOL _DataNumReg::SetValuesInt(
    [in] LONG Index,
    [in, out] LONG* Value,
    [in] LONG Count
);

With the parameter Value being a pointer to the first element of a C-style array.
My idea was to create a C array in Python using the ctypes library, and use the ctypes.addressof() function to get the pointer to the array,
and then pass this pointer to the COM interface with win32com.

The issue, as you might've guessed is that win32com automatically creates a new pointer to, what already is a pointer.
This was already mentioned earlier in 2013, https://mail.python.org/pipermail/python-win32/2013-May/012821.html

In which is told that "passing the address of a Python integer object clearly isn't correct - or to put it another way - what exact are you hoping to pass as this parameter?",
while for my specific case, passing a Python integer IS correct, as it is already a valid pointer.

Because the COM library is closed source I can't change it to expect a pointer to a pointer, so as far as I can come up with, my only solutions left are:
A. Write a Win32 DLL wrapper that can call the COM interface.
B. Change the win32com library myself to stop creating pointers automatically, or accept a Python list, copy it to a buffer, and send a pointer to that buffer.
C. Hope that you might have more advice or information I missed.


I already tried changing the .py wrapper generated by makepy.py to hopefully make win32com think that the COM interface requires a VT_UI4/VT_I4 instead of the generated VT_BYREF | VT_I4, but that didn't work, the behavior of win32com creating a pointer to a pointer was still occurring. Nor did changing the [in, out] (3) to [in] (1) in the .py wrapper help.

Can you give me any more advice/tricks on how to make the COM interface receive a pointer to a C-array instead of a single value, preferably using win32com?


Any information is greatly appreciated.

Regards,
Simon van Bezooijen
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