Python script that'll convert MIDI message strings to channel number (G#1 -> 44)

convert_midi.py

'''
Convert midi message into number

C-2 -> 0
G8 - 127

Supports Korg/Roland/synths with alternative starting octaves
    * Example: In korg/roland synths, the low C is C-1(#0) and high G is G9(#127)
'''

_NOTES = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B']


def midi_to_note_number(midi:str, octave_min=-2):
    """
    Given a midi note string, return that notes channel number

        * Note - kwarg 'octave_min' should be used when the minimum octave count for your keyboard/controller/synth etc.
                is known and not equal to the default value: -2
                Examples here are KORG and Roland synths

    :param str midi: A string that holds note, accidental and octave ex. C#1
    :param int octave_min: Optional, minimum octave of the note range.
    :return: int
    """
    note_index, octave = _get_note_parts(midi)
    normalized_octave = octave_min - octave
    return abs(normalized_octave * 12) + note_index


def _get_note_parts(midi:str):
    """
    Given a midi note, get its note and octave

    Note conversion example
    C-2 -> 0, -2
    C#-2 -> 1, -2
    ...
    E0-> 4, 0
    ...
    B4 -> 11, 4
    etc..

    :param str midi: A string that holds note, accidental and octave
    :return: [note: int, octave: int]
    """
    if '#' in midi:
        note = midi[:2]
        octave = int(midi[2:])
    else:
        note = midi[0]
        octave = int(midi[1:])
    try:
        note_index = _NOTES.index(note)
    except ValueError:
        raise RuntimeError('Invalid midi note passed. {0}. '
                           'Must match convention <note><accidental><octave> (ex. C#-1)'.format(midi))
    return note_index, octave


if __name__ == '__main__':
    # tests
    print("Midi Note Conversion Tests: ")
    print(midi_to_note_number("G#1"))
    print(midi_to_note_number("C-2") == 0, midi_to_note_number("G8") == 127)

    print("Midi Note Conversion Tests: octave min = -1")
    print(midi_to_note_number("G#1", octave_min=-1))
    print(midi_to_note_number("G9", octave_min=-1))
    print(midi_to_note_number("C-1", octave_min=-1) == 0, midi_to_note_number("G9", octave_min=-1) == 127)