I also started out with some python code for this 
but then thought since I already have all structures defined in dfuse.c it would probably be faster to carve something out from there in c. And then I realized it would be much faster to implement raw binary download in dfuse.c so that’s where I left it at now. So your script would be welcome!
You have the DfuSe file specification UM391, right? It should not be necessary to reverse-engineer the existing DfuSe files.