What is the significance of this traceback? I tried to use the add-ons to export elements from a Blender file to the ~.dxf format, and after attempting the export, I tried to re-import the ~.dxf file to make certain that it was working properly. It was apparently was not. Looking at the console window, the export appeared to work fine, but the re-import failed, giving me this traceback:

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I know what the traceback is, but I don't know how to understand what it means.
I still don't know how to interpret the traceback, but I found out what triggered it. I exported the elements of the original ~.blend file to ~.dxf format one by one, with all but one of them exporting successfully. The problem triggering the failure of the import turned out to be in one portion of export, where there was one duplicate vertex, which I removed by using the "remove doubles" special menu option. After removing the stray vertex, the formerly misbehaving element exported normally, with no error and no traceback.