New in version 2.0.
Analyze expr and return tonal function according to key_signature.
abjad> from abjad.tools import tonalitytools
abjad> chord = Chord(['ef', 'g', 'bf'], (1, 4))
abjad> key_signature = contexttools.KeySignatureMark('c', 'major')
abjad> tonalitytools.analyze_tonal_function(chord, key_signature)
FlatIIIMajorTriadInRootPosition
Return none when no tonal function is understood.
abjad> chord = Chord(['c', 'cs', 'd'], (1, 4))
abjad> key_signature = contexttools.KeySignatureMark('c', 'major')
abjad> tonalitytools.analyze_tonal_function(chord, key_signature) is None
True
Return tonal function or none.