pushing Python list value as COM parameter only sends NA/Empty values

[syoo47]

I'm using Python 3.9.4 64-bit, with comtypes library 1.1.10. Making a method call on a COM object with a list variable as a parameter results in an empty VARIANT array to be received by the COM object. The array has the right number of elements to match the original list object, but each element is empty/NA.

This was also happening with comtypes library 1.1.8.

[syoo47]

Did some more testing. comtypes library only seems to fail on python 3.8 or above. 3.7 works just fine.

[vasily-v-ryabov]

Looks like duplication of #212

[syoo47]

vasily, thanks for the heads up. I was able to test your suggested workaround (using tagVARIANT) and it seems to work now under Python 3.9. Thanks again!

[vasily-v-ryabov]

@syoo47 can you attach your C++ example code that can reproduce the issue without any debugger?

[syoo47]

It would be hard to provide the C++ code for this as it's an entire COM Automation server and is fairly large. I'd have to create an entire test automation server in order to reproduce this issue.

Besides, it's not a problem on the C++ side (com server). It's a problem on the python side (com client) that is trying to push a simple list array as a single parameter to the com object using comtypes library. On the C++ side, the variant is received as an array with the right number of elements, but each element is empty. By converting the list object explicitly to a tagVARIANT object, the COM call now works:

#the following sends an empty array list
col_data = obj[col].tolist()
app.PutSeries(col, col_data)

#the following sends the appropriate array data
col_data = automation.tagVARIANT(obj[col].tolist())
app.PutSeries(col, col_data)

If you want to reproduce this, get a demo license for EViews, then download and install the pyeviews-1.0.2 python library (not the latest), and then try the examples mentioned in the pyeviews documentation.

[vasily-v-ryabov]

@syoo47 thanks! I will make next attempt next week.