Evan, IDLE runs your code with the Python running IDLE.  Bad tracebacks are created by Python and are usually, as in this case, the fault of Python.  To decide, run your code directly with Python, at a command line, instead of indirectly with IDLE, and see if you get the same problem.  

In this case, I ran, on Windows, in Command Prompt, 'py -m a.tem3', where 'py' defaults to python 3.7.1 and 'a' is a directory on sys.path.