For the next tag update I have dwipreproc internally executing eddy_quad if -eddyqc_text or -eddyqc_all is specified. It’s a little difficult to get a traceback, but you can see the final resulting code here. Maybe there might be some clue there as to how to get it working. I do seem to have documented in a comment there that QUAD does not work with Python2 (at least it didn’t when I wrote the code), but the exception you’re seeing doesn’t appear to be related to Python version.
It’s more likely to have something to do with fine names. I’m pretty sure that the DWI - “B1000_dc.nii.gz” in your case - and the additional files that are written by eddy and read by the eddy_quad command - here exported to a directory “B1000_eddyQC/” - need to have the same basename; i.e. differ in file extension only.