New in version 2.0.
Get arithmetic mean of chromatic pitch number of pitches in chord:
abjad> chord = Chord("<g' c'' e''>4")
abjad> chordtools.get_arithmetic_mean_of_chord(chord)
11.666666666666666
Return none when chord is empty:
abjad> chord = Chord("< >4")
abjad> chordtools.get_arithmetic_mean_of_chord(chord) is None
True
Return number or none.