midi.py: Convert midi.midi_callbacks to a set.

tulip/shared/py/midi.py

@@ -471,15 +471,14 @@ def midi_event_cb(midi_message):
 
 
 
-midi_callbacks = {}
+midi_callbacks = set()
 
 # Add a midi callback and return a slot number
 def add_callback(fn):
- midi_callbacks[fn] = True
+ midi_callbacks.add(fn)
 
 def remove_callback(fn):
- if fn in midi_callbacks:
- del midi_callbacks[fn]
+ midi_callbacks.remvoe(fn)
 
 def start_default_callback():
  add_callback(midi_event_cb)
@@ -488,13 +487,12 @@ def stop_default_callback():
  remove_callback(midi_event_cb)
 
 
-
 # The midi callback sent over from C, fires all the other ones if set.
 def c_fired_midi_event(x):
  m = tulip.midi_in() 
  while m is not None and len(m) > 0:
  # call the other callbacks
- for c in midi_callbacks.keys():
+ for c in midi_callbacks:
  c(m)
 
  # Are there more events waiting?