The comments about harmonicas can also apply to whistles where the key of the whistle is not neccessarily the key of the tune played. Many tune sets are played with perhaps one tune being in G and another in D, and some tunes (especially polkas) change key for the different sections. A whistle player would therefore use the same instrument and play accidentals as required.

I have met quite a few whistle players who have told me that a tune is in D because that is the key of whistle that they are playing it on - when they are actually playing it in G.