Raspberry Piano synth

synth.py

#!/usr/bin/env python

import RPi.GPIO as GPIO
import time
import subprocess
from os import path
from os import listdir
import sys
import threading

GPIO.setmode(GPIO.BCM)

GPIO.setup(23, GPIO.IN, pull_up_down=GPIO.PUD_UP)
GPIO.setup(24, GPIO.IN, pull_up_down=GPIO.PUD_UP)
GPIO.setup(25, GPIO.IN, pull_up_down=GPIO.PUD_UP)

sound_fonts_dir = path.join(path.dirname(path.realpath(sys.argv[0])), 'fonts')
sound_fonts = [f for f in listdir(sound_fonts_dir) if path.isfile(path.join(sound_fonts_dir, f))]

sound_font_index = sound_fonts.index("Full Grand Piano.sf2")
fsynth_process = None

def is_running():
    global fsynth_process
    return fsynth_process != None and fsynth_process.poll() == None

def kill_process():
    global fsynth_process
    if not is_running():
        fsynth_process = None
        return
    fsynth_process.kill()
    fsynth_process.wait()
    fsynth_process = None

def connect_thread_func():
    time.sleep(.200)
    for i in range(20):
        if subprocess.call(['aconnect', '24:0', '128:0']) == 0:
            break
        time.sleep(.500)

def start_process():
    global fsynth_process, sound_fonts, sound_font_index
    if is_running():
        kill_process()
    sound_font = path.join(sound_fonts_dir, sound_fonts[sound_font_index])
    print('Using sound font: ' + sound_font)
    fsynth_process = subprocess.Popen(['fluidsynth', '-a', 'alsa', '-is', sound_font])
    t = threading.Thread(target=connect_thread_func)
    t.start()

def on_toggle(channel):
    if is_running():
        kill_process()
    else:
        start_process()

def on_next(channel):
    global sound_font_index, sound_fonts
    if is_running():
        sound_font_index = (sound_font_index + 1) % len(sound_fonts)
        start_process()

def on_prev(channel):
    global sound_font_index, sound_fonts
    if is_running():
        sound_font_index = (sound_font_index - 1) % len(sound_fonts)
        start_process()

GPIO.add_event_detect(25, GPIO.RISING, callback=on_toggle, bouncetime=100)
GPIO.add_event_detect(24, GPIO.RISING, callback=on_next, bouncetime=100)
GPIO.add_event_detect(23, GPIO.RISING, callback=on_prev, bouncetime=100)

while True:
    time.sleep(10000)