SystemError: error return without exception set

[Chris Angelico]

On Fri, Dec 8, 2017 at 2:36 AM, Natalie Leung <natalieleung.29 at gmail.com> wrote:
> I am trying to use Python to communicate and send commands in MSC Marc. A part of the code looks something like this:
>
> from py_mentat import*
>
> directory = '[specified the file path to my model]'
> marcModel = '[name of my model]'
>
> py_echo(0)
> openModel = '*new_model yes *open_model "'+ directory + marcModel +'"'
> py_send(openModel)
>
>
> The code stops at "py_send(openModel)" with an error message that reads: Traceback (most recent call last): File "[my file path]", line 11, in py_send(openModel)
> SystemError: error return without exception set
>
> I tried running the code on different platforms (e.g. Command Prompt, Wing 101, python.exe) and I get the same result. What could be the problem?

In its purest sense, that error is a bug inside a Python extension
module (as others have mentioned). Since the failure is basically
"hey, you said you raised an exception, but I can't find the exception
you thought you were raising", it's quite probable that there is a bug
in your Python code; go back to the tutorial for Marc, and see if you
can find an issue. Unfortunately you're flying blind here, but maybe
you can figure something out even without the usual help of the error
message.

But regardless, the bug first and foremost is in the extension module.
The module's creator should be able to audit the py_send function to
figure out where it is returning NULL without calling one of the
"raise exception" functions.

ChrisA