SuSE have actually packaged python-xml separately, even though it "should" be baked-in to python >= 2.0. This means it is possible (although perhaps not very likely) that the xml module could be missing. Currently, this makes tl-setup explode with tracebacks all over the place when zypperbackend tries to import the xml module. If we want to be really ambitious, perhaps we could catch ImportErrors here.
*** Bug 7357 has been marked as a duplicate of this bug. ***
This is no longer an issue now that we switched to Python 3. The xml modules is now packaged with Python as it should be.