Could it have been based on Eddie Lang...?
I'm listening to an Eddie Lang CD right now, just saw it at Amoeba Records in Hollywood while searching out Jazz CD's and picked it up, and well, gee, it sounds like Django lite, a little bit of the Gypsy stuff in there, but his own playing for sure.
Mr. Lang's a real good player, don't get me wrong. What interests me is that he was in his hay-day in the mid ‘20’s to early '30's so... maybe Penn's character was based a bit on this guy? Right time, right place….?
Good player for sure, lived a too short life:
http://en.wikipedia.org/wiki/Eddie_Lang