[WxPython] NameError: global name 'PyAssertionError' is not defined

[merlem]

the error indicates that the value of dyn (which I assume is the column number)  is out or range.

Yes, that's the case, but it's not my question.
I know where the PyAssertionError comes from. But where does the NameError comes from?

And does it really need a snippet for a (basically theoretical) question why the own errors are not known to python and how to handle this? But I'll prepare one. May take some hours, then I'll send it.