Fix scale_diagram enharmonic matching — v0.43.1

Scale notes spelled with flats (e.g. the Eb blue note in the blues
scale) were silently dropped from scale_diagram() because the fretboard
spells that pitch as D#, so the string comparison never matched. Match
notes enharmonically via the system's canonical name and display them
using the scale's own spelling. Pre-existing bug (also in 0.42.x),
surfaced while flipping the docs for the low-to-high release.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -2,6 +2,14 @@
 
 All notable changes to PyTheory are documented here.
 
+## 0.43.1
+
+- **Fix `Fretboard.scale_diagram()` enharmonic matching.** Scale notes
+  spelled with flats (e.g. the `Eb` blue note in the blues scale) were
+  silently omitted from the diagram, because the fretboard spells that
+  pitch as `D#`. Notes are now matched enharmonically (by pitch) and
+  displayed using the scale's own spelling.
+
 ## 0.43.0
 
 - **BREAKING — fingerings now read low-to-high by default.** `Fretboard`

docs/guide/nashville-blues-tabs.rst

@@ -208,12 +208,12 @@ Visualize the blues scale on guitar to see the patterns:
    >>> blues = TonedScale(tonic="A4", system="blues")["blues"]
    >>> print(fb.scale_diagram(blues, frets=12))
        0   1   2   3   4   5   6   7   8   9  10  11  12
-   E| - | - | - | - | - | A | - | - | C | - | D | Eb| E |
+   E| E | - | - | G | - | A | - | - | C | - | D | Eb| E |
-   A| A | - | - | C | - | D | Eb| E | - | - | - | - | A |
+   A| A | - | - | C | - | D | Eb| E | - | - | G | - | A |
-   D| - | - | - | - | A | - | - | C | - | D | Eb| E | - |
+   D| D | Eb| E | - | - | G | - | A | - | - | C | - | D |
-   G| - | - | A | - | - | C | - | D | Eb| E | - | - | - |
+   G| G | - | A | - | - | C | - | D | Eb| E | - | - | G |
-   B| - | - | - | D | Eb| E | - | - | - | - | A | - | - |
+   B| - | C | - | D | Eb| E | - | - | G | - | A | - | - |
-   E| - | - | - | - | - | A | - | - | C | - | D | Eb| E |
+   E| E | - | - | G | - | A | - | - | C | - | D | Eb| E |
 
 The minor pentatonic (same scale without the Eb) is the most-played
 scale in rock guitar. Add the blue note and you have the full blues

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "pytheory"
-version = "0.43.0"
+version = "0.43.1"
 description = "Music Theory for Humans"
 readme = "README.md"
 license = "MIT"

pytheory/__init__.py

@@ -1,6 +1,6 @@
 """PyTheory: Music Theory for Humans."""
 
-__version__ = "0.43.0"
+__version__ = "0.43.1"
 
 from .tones import Tone, Interval
 from .systems import System, SYSTEMS, TET

pytheory/chords.py

@@ -1867,10 +1867,24 @@ class Fretboard:
             >>> am = Chord.from_symbol("Am")
             >>> print(fb.scale_diagram(pentatonic, frets=5, chord=am))
         """
-        scale_notes = set(scale.note_names)
+        # Match notes enharmonically: the fretboard spells tones with
+        # sharps (e.g. D#), but a scale may use flats (e.g. Eb). Compare
+        # via the system's canonical name so Eb and D# count as the same
+        # pitch — and display using the scale's own spelling.
+        _system = self._tones[0].system
+        def _resolve(name):
+            resolved = _system.resolve_name(name)
+            return resolved if resolved is not None else name
+
+        # Map canonical pitch -> the scale's preferred spelling for display.
+        scale_display = {}
+        for n in scale.note_names:
+            scale_display.setdefault(_resolve(n), n)
+        scale_notes = set(scale_display)
+
         chord_notes = set()
         if chord is not None:
-            chord_notes = {t.name for t in chord.tones}
+            chord_notes = {_resolve(t.name) for t in chord.tones}
 
         max_name = max(len(t.name) for t in self.tones)
         lines = []
@@ -1885,13 +1899,15 @@ class Fretboard:
             fret_marks = []
             for f in range(frets + 1):
                 note = tone.add(f)
-                if note.name in scale_notes:
+                key = _resolve(note.name)
-                    if chord_notes and note.name in chord_notes:
+                if key in scale_notes:
-                        fret_marks.append(f" {note.name.upper():<2s}")
+                    label = scale_display[key]
+                    if chord_notes and key in chord_notes:
+                        fret_marks.append(f" {label.upper():<2s}")
                     elif chord_notes:
-                        fret_marks.append(f" {note.name.lower():<2s}")
+                        fret_marks.append(f" {label.lower():<2s}")
                     else:
-                        fret_marks.append(f" {note.name:<2s}")
+                        fret_marks.append(f" {label:<2s}")
                 else:
                     fret_marks.append(" - ")
             line = f"{tone.name:>{max_name}}|{'|'.join(fret_marks)}|"

test_pytheory.py

@@ -3522,6 +3522,19 @@ def test_scale_diagram():
     assert len(lines) == 7
 
 
+def test_scale_diagram_enharmonic_flat_note():
+    """A flat-spelled scale note (e.g. the blues Eb) must render even
+    though the fretboard spells that pitch as D#."""
+    fb = Fretboard.guitar()
+    blues = TonedScale(tonic="A4", system="blues")["blues"]
+    assert "Eb" in blues.note_names
+    diagram = fb.scale_diagram(blues, frets=12)
+    # The blue note shows up using the scale's own (flat) spelling,
+    # never the fretboard's sharp spelling.
+    assert "Eb" in diagram
+    assert "D#" not in diagram
+
+
 # ── Coverage gap tests ─────────────────────────────────────────────────────
 
 def test_tone_init_octave_parsed_from_name():

uv.lock

@@ -690,7 +690,7 @@ wheels = [
 
 [[package]]
 name = "pytheory"
-version = "0.43.0"
+version = "0.43.1"
 source = { editable = "." }
 dependencies = [
     { name = "rich" },