I'm teaching myself the solo to Djangology (1935), and I'm at the point where Django starts a series of half-step trills, which are picked rather than hammered. This begins slowly in measure sixteen of Dennis's transcription and speeds up in subsequent measures.
I'm guessing that the best way to play this is by sliding one finger rapidly up and down over the fret while alternate picking. I think Bireli Lagrene did that when I saw him a couple of weeks ago. Am I right?
I can see that it's going to take quite a few hours to nail down this little gypsy trick!