According to the description, where is my money? 😉

U just is Jedi of Python code @_@

Even though I took this approach, I wouldn't count it as a best practice. It sacrifices some time complexity for readability.

how this can be an answer
WHAT

Interesting problem. If I hadn't studied music I would not have been able to solve this. I agree with others that it should be explained clearer. It doesn't require too much music theory, just a little, for the average CW user to be able to figure this out.

Might be an enhancement later to have the coder solve how to differentiate between sharps and flats for the appropriate keys.

All that said, I enjoyed this problem. Bravo!

@vivekpontoosh: in terms of Bb, there is no suspended 4th in this case. The 3rd of a Bb chord would be some kind of D, such as Db for Bb minor or D for Bb major. If there were a 4th for a Bb chord, then we would encounter an Eb in the chord. Simply put, Bb G D reesults in a 1st inversion G minor chord.

A# is enharmonic (equivalent) to B-flat major.
(A# isn't used much because of all of the accidentals and double-sharps)
A# is an artifact from using the midi tables.

And if you look at this in Bb terms, it comes out to:
Bb G D, which is a raised 3rd (of 4th, or suspended)
which isn't a major triad

The major triad would be: Bb F D

And what about float('inf')?

I'm fucking stupid and have started coding 2 seconds ago, can anyone explain how it works?
It is not covering all case scenarios and I think I will learn wrong because of that.

Neat. Best Practice + Clever. I wish to give both to this.

I wish there was a way to down vote solutions

Right, thanks.