I read your explanation in relation to the code and got part of it but not all. I need to try another run through. I may try to locally (and temporarily), print to the console to see what is happening.

I am also not clear on the relation between the UnicodeDecodeError and tuple splitting. Does '_flatten((self._w, cmd)))' call split or splitlist on the tuple arg? Is so, do you know why a problem with that would lead to the UDError? Does your patch fix the leading '0' regression?