One never knows what one can find at a Paris street market...
Perhaps a book of Beethoven Sonatas or Alkan's Le Chemin de fer?
I would have snatched up Chopin's Polonaise in A flat Major, Opus 53
When I was walking that Sunday on a narrow street, I could hear strains of piano music from an accomplished student. The long passageway amplified the tones to a dreamlike state, and I felt that I should tiptoe so as not to break the spell.