Music XML

generator/harmony.py

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+from __future__ import annotations
+
+from generator.model import NATURAL, parse_pitch_name, pitch_name
+
+# Semantic degrees are independent of guitar voicing omissions.
+KINDS = {
+  'major': {1:0, 3:0, 5:0}, 'minor': {1:0, 3:-1, 5:0},
+  'augmented': {1:0, 3:0, 5:1}, 'diminished': {1:0, 3:-1, 5:-1},
+  'dominant': {1:0, 3:0, 5:0, 7:-1}, 'major-seventh': {1:0, 3:0, 5:0, 7:0},
+  'minor-seventh': {1:0, 3:-1, 5:0, 7:-1}, 'diminished-seventh': {1:0, 3:-1, 5:-1, 7:-2},
+  'augmented-seventh': {1:0, 3:0, 5:1, 7:-1}, 'augmented-major-seventh': {1:0, 3:0, 5:1, 7:0},
+  'half-diminished': {1:0, 3:-1, 5:-1, 7:-1}, 'major-minor': {1:0, 3:-1, 5:0, 7:0},
+  'major-sixth': {1:0, 3:0, 5:0, 6:0}, 'minor-sixth': {1:0, 3:-1, 5:0, 6:0},
+  'suspended-second': {1:0, 2:0, 5:0}, 'suspended-fourth': {1:0, 4:0, 5:0},
+  'power': {1:0, 5:0}, 'pedal': {1:0}, 'other': {}, 'none': {},
+  'Neapolitan': {1:0, 3:0, 5:0}, 'Italian': {1:0, 3:0, 6:1},
+  'French': {1:0, 3:0, 4:1, 6:1}, 'German': {1:0, 3:0, 5:0, 6:1},
+}
+for family, base in (('dominant', 'dominant'), ('major', 'major-seventh'), ('minor', 'minor-seventh')):
+  for suffix, highest in (('ninth',9), ('11th',11), ('13th',13)):
+    KINDS[f'{family}-{suffix}'] = {**KINDS[base], **{i:0 for i in range(9, highest+1, 2)}}
+
+SUFFIXES = {'major':'', 'minor':'-', 'augmented':'+', 'diminished':'dim', 'dominant':'7', 'major-seventh':'maj7', 'minor-seventh':'-7', 'diminished-seventh':'dim7', 'augmented-seventh':'+7', 'augmented-major-seventh':'+maj7', 'half-diminished':'-7b5', 'major-minor':'-maj7', 'major-sixth':'6', 'minor-sixth':'-6', 'suspended-second':'sus2', 'suspended-fourth':'sus4', 'power':'5', 'pedal':'', 'other':''}
+for family, prefix in (('dominant',''), ('major','maj'), ('minor','-')):
+  for suffix, number in (('ninth','9'), ('11th','11'), ('13th','13')):
+    SUFFIXES[f'{family}-{suffix}'] = prefix + number
+
+
+def degrees(harmony: dict) -> dict[int, int]:
+  kind = harmony['kind']
+  if kind not in KINDS:
+    raise ValueError(f'unsupported harmony kind: {kind}')
+  result = KINDS[kind].copy()
+  for change in harmony.get('degrees', []):
+    degree, alter, operation = change['value'], change['alter'], change['type']
+    if type(degree) is not int or degree < 1 or type(alter) is not int:
+      raise ValueError('invalid harmony degree')
+    if operation == 'subtract':
+      if degree not in result:
+        raise ValueError(f'cannot subtract absent chord degree {degree}')
+      del result[degree]
+    elif operation == 'alter':
+      if degree not in result:
+        raise ValueError(f'cannot alter absent chord degree {degree}; use add')
+      result[degree] = alter
+    elif operation == 'add':
+      if degree in result:
+        raise ValueError(f'duplicate added chord degree {degree}')
+      result[degree] = alter
+    else:
+      raise ValueError(f'unsupported degree operation: {operation}')
+  if kind != 'none' and not result:
+    raise ValueError('harmony contains no pitch information')
+  return result
+
+
+def degree_semitones(degree: int, alter: int) -> int:
+  return 12 * ((degree-1)//7) + (0,2,4,5,7,9,11)[(degree-1)%7] + alter
+
+
+def pitch_classes(harmony: dict) -> tuple[int, ...]:
+  if harmony['kind'] == 'none':
+    return ()
+  root = harmony['root']
+  root_pc = NATURAL[root['letter']] + root['alter']
+  values = [(root_pc + degree_semitones(d, a)) % 12 for d, a in degrees(harmony).items()]
+  if bass := harmony.get('bass'):
+    values.append((NATURAL[bass['letter']] + bass['alter']) % 12)
+  return tuple(dict.fromkeys(values))
+
+
+def symbol(harmony: dict) -> str:
+  if harmony['kind'] == 'none':
+    return 'N.C.'
+  suffix = harmony.get('kind_text', SUFFIXES.get(harmony['kind'], harmony['kind']))
+  if 'kind_text' not in harmony:
+    for d in harmony.get('degrees', []):
+      sign = '#' * max(d['alter'], 0) + 'b' * max(-d['alter'], 0)
+      suffix += ('no' if d['type']=='subtract' else 'add' if d['type']=='add' and not sign else '') + sign + str(d['value'])
+  result = pitch_name(harmony['root']) + suffix
+  if bass := harmony.get('bass'):
+    result += '/' + pitch_name(bass)
+  return result
+
+
+def parse_symbol(text: str) -> dict:
+  import re
+  match = re.fullmatch(r'([A-Ga-g][#b]*)([^/]*)(?:/([A-Ga-g][#b]*))?', text.strip())
+  if not match:
+    raise ValueError(f'invalid chord symbol: {text!r}')
+  root, suffix, bass = match.groups()
+  aliases = {'m':'minor', 'min':'minor', 'maj':'major', 'M':'major', 'm7':'minor-seventh', 'm6':'minor-sixth', 'm7b5':'half-diminished', 'o':'diminished', 'o7':'diminished-seventh', 'aug':'augmented', 'sus':'suspended-fourth'}
+  aliases.update({v:k for k,v in SUFFIXES.items() if k not in ('other','pedal')})
+  core = suffix
+  changes = []
+  while core not in aliases:
+    m = re.search(r'(add|no)?([b#]?)(\d+)$', core)
+    if not m:
+      raise ValueError(f'unsupported chord spelling: {text!r}')
+    op, accidental, value = m.groups()
+    changes.insert(0, {'value':int(value), 'alter':1 if accidental=='#' else -1 if accidental=='b' else 0, 'type':'subtract' if op=='no' else 'add'})
+    core = core[:m.start()]
+  kind = aliases[core]
+  for d in changes:
+    if d['type']=='add' and d['value'] in KINDS[kind]:
+      d['type'] = 'alter'
+  result = {'root':parse_pitch_name(root), 'kind':kind, 'degrees':changes, 'kind_text':suffix}
+  if bass:
+    result['bass'] = parse_pitch_name(bass)
+  degrees(result)
+  return result