Yes, in Db (5 flats). But at the key change, it goes into E major (4 sharps). In impressionistic music, key changes don't necessarily follow earlier rules. Why E? Two measures before the key change, the first two beats center around a Db chord; the third beat is an Fb chord. This repeats the measure before the key change. But the third chord is E. It sounds the same as an Fb chord, just spelled differently.
The Fb chord amounts to a major chord, but a minor third above Db, the key the piece is in. Fb major is a really clumsy key to write out, so Chopin put it into its sharp equivalent, E major.
I haven't looked into how he gets from E major back into Db major, but he does. Db isn't too hard on a C solo tuned harmonica, but E (4 sharps) is trickier. However, learning it from tablature may actually be easier, as long as the tab matches the melody of the original.
Tom