Decode received MIDI RPN messages

recvrpn.py

import time
from collections import defaultdict

import rtmidi
from rtmidi.midiconstants import *
from rtmidi.midiutil import open_midiinput


class RPNDecoder:
    def __init__(self, channel=1):
        self.channel = (channel - 1) & 0xF
        self.rpn = 0
        self.values = defaultdict(int)
        self.last_changed = None

    def __call__(self, event, data=None):
        msg, deltatime = event

        # event type = upper four bits of first byte
        if msg[0] == (CONTROL_CHANGE | self.channel):
            cc, value = msg[1], msg[2]
            if cc == RPN_LSB:
                self.rpn = (self.rpn >> 7) * 128 + value
            elif cc == RPN_MSB:
                self.rpn = value * 128 + (self.rpn & 0x7F)
            elif cc == DATA_INCREMENT:
                self.set_rpn(self.rpn, min(2 ** 14, self.values[self.rpn] + 1))
            elif cc == DATA_DECREMENT:
                self.set_rpn(self.rpn, max(0, self.values[self.rpn] - 1))
            elif cc == DATA_ENTRY_LSB:
                self.set_rpn(self.rpn, (self.values[self.rpn] >> 7) * 128 + value)
            elif cc == DATA_ENTRY_MSB:
                self.set_rpn(self.rpn, value * 128 + (self.values[self.rpn] & 0x7F))

    def set_rpn(self, rpn, value):
        self.values[rpn] = value
        self.last_changed = rpn

decoder = RPNDecoder()
m_in, port_name = open_midiinput()
m_in.set_callback(decoder)

while True:
    rpn = decoder.last_changed
    if rpn:
        print("RPN %i: %i" % (rpn, decoder.values[rpn]))
        decoder.last_changed = None
    time.sleep(0.1)

Latest version: https://github.com/SpotlightKid/python-rtmidi/blob/master/examples/advanced/recvrpn.py