I want to be able to define chords using standard chord notation

[ntoll]

Names like "Dmaj7", "F13", "Csus4" etc are used by musicians to define a harmonic block, aka a chord. I should be able to use such terms as a harmonic DSL that returns a data structure defining the constituent notes. Such a data structure could then be given to, say, a generator function to produce actual pitches or melodic fragments that work for the named chord. Other meta-data (such as the chord's inversion) could be passed in on init.

Sample code, as a starter for 10:

>>> my_chord = music.chord("Dmaj7", inversion=root)
>>> my_chord
<Chord: Dmaj7 root>
>>> chord.notes
["d", "f#", "a", "c#"]
>>> chord.inversion
"root"

[lordmauve]

Do you have a spec for the chord naming scheme here? I've gone from https://en.wikipedia.org/wiki/Chord_names_and_symbols_(popular_music) but I don't know very much music theory and it's likely I've made mistakes even in what I've implemented (here).

[ntoll]

So... music theory is very complicated and context is always a big factor. So you can't just have "solution X" because that will only work in certain specific situations (I notice the article to which you link is for chord names in popular music.... add in Classical or, heaven forbid, Jazz [where it gets VERY complicated] and your problem space just exploded).

Here's a taster of what I mean:

• The chord Gm7 (G minor with an added seventh) has the notes, G, Bb, D and F.
• The chord Bb6 (B6 major with an added sixth) has the notes (you guessed it), Bb, D, F and G.
• The "set" of notes is exactly the same.
• Which chord we're using depends on:
  • The key (a whole can of worms I don't have time to explain),
  • The inversion of the chord (i.e. which of the constituent notes is lowest),
  • The harmonic context (is this a IV, V, I cadence in D minor, or a IV, V, I cadence in F major?),
  • The voicing (to some extent) -- i.e. how the notes a spread out and/or repeated on top of each other.
  • The mood of the composer, because they just use Gm7 rather than Bb6 as an aesthetic judgement for the purposes of reading chord symbols.
  • ....
  • (You get the idea)

Taking off my musician's cap and putting on my coder's top hat...

It is fruitless to try to cover all possible combinations of notes and chord names for the reasons outlined above. However, you could just provide the most common ones as instances of a generic Chord class/data structure that folks could happily use to define their own chords given the complicated context in which they find themselves. The most important aspect of this is the Chord class should behave in an expected way when combined with other musical/code abstractions. For instance, a ChordSequence class would be, in a sense, an ordered collection of Chord instances -- which would make perfect sense to a musician. Furthermore, individual chords are managed in the Chord instances, whereas the interactions / context of the chords when played next to each other are dealt with in the ChordSequence instance. I guess I'm saying we should make sure we name, use and define the expected abstractions.