Shared Catalog

generator/transposition.py

@@ -78,6 +78,12 @@ def shift_key(key: dict, steps: int, semitones: int) -> dict:
         break
     else:
       result['custom'] = True
+  if 'cancel' in key:
+    # A cancellation references the old signature, not a count of naturals.
+    cancelled = shift_key(key_from_fifths(key['cancel']), steps, semitones)
+    if cancelled.get('custom'):
+      raise ValueError('transposed key cancellation cannot be represented by fifths')
+    result['cancel'] = cancelled['fifths']
   return result
 
 def transposition_interval(document: dict, target_key_name: str) -> tuple[int, int]: