Hand back a new pitch from getPitchFromNodeDegree

music21/scale/__init__.py

@@ -557,7 +557,7 @@ def getPitchFromNodeDegree(self,
             alteredDegrees=self._alteredDegrees,
             equateTermini=equateTermini
         )
-        return copy.deepcopy(post)
+        return post
 
     def realizePitchByDegree(self,
                              pitchReference: _PitchOrStr,
@@ -654,7 +654,7 @@ def getNewTonicPitch(self,
             maxPitch=maxPitch,
             alteredDegrees=self._alteredDegrees
         )
-        return copy.deepcopy(post)
+        return post
 
     # --------------------------------------------------------------------------
 

music21/scale/intervalNetwork.py

@@ -2707,15 +2707,16 @@ def getPitchFromNodeDegree(
                 # environLocal.printDebug(['comparing', realizedNId,
                 #   'nodeTargetId', nodeTargetId])
 
+                # realizedPitch may be a cached realization: hand back a copy
                 if realizedNId == nodeTargetId.id:
-                    return realizedPitch[i]
+                    return copy.deepcopy(realizedPitch[i])
                 # NOTE: this condition may be too generous, and was added to solve
                 # a non-tracked problem.
                 # only match this generously if we are equating termini
                 if equateTermini:
                     if ((realizedNId in (Terminus.HIGH, Terminus.LOW))
                             and (nodeTargetId.id in (Terminus.HIGH, Terminus.LOW))):
-                        return realizedPitch[i]
+                        return copy.deepcopy(realizedPitch[i])
 
             # environLocal.printDebug(['getPitchFromNodeDegree() on trial', trial, ',
             #    failed to find node', nodeTargetId])

music21/scale/test_intervalNetwork.py

@@ -627,6 +627,28 @@ def test_realize_descending_reversed_cached(self):
         self.assertEqual(descending_melodic_minor_reversed[0].nameWithOctave, 'C4')  # was B-4
         self.assertEqual(descending_melodic_minor_reversed[-1].nameWithOctave, 'B-4')  # was C4
 
+    def test_get_pitch_from_node_degree_returns_a_new_pitch(self):
+        '''
+        A realization may be held in _ascendingCache or _descendingCache, so
+        the pitch taken out of one has to be the caller's own -- otherwise
+        writing to it edits the cached scale.
+        '''
+        net = IntervalNetwork()
+        net.fillBiDirectedEdges(['M2', 'M2', 'm2', 'M2', 'M2', 'M2', 'm2'])
+
+        first = net.getPitchFromNodeDegree('c4', 1, 1)
+        self.assertEqual(first.nameWithOctave, 'C4')
+        first.octave = 1
+
+        again = net.getPitchFromNodeDegree('c4', 1, 1)
+        self.assertEqual(again.nameWithOctave, 'C4')
+
+    def test_next_pitch_does_not_move_a_cached_degree(self):
+        sc = scale.RagAsawari('c4')
+        self.assertEqual(str(sc.pitchFromDegree(1)), 'C4')
+        self.assertEqual(str(sc.nextPitch('c1', Direction.ASCENDING)), 'D1')
+        self.assertEqual(str(sc.pitchFromDegree(1)), 'C4')
+
 
 # ------------------------------------------------------------------------------
 if __name__ == '__main__':

music21/scale/test_scale_main.py

@@ -456,7 +456,7 @@ def testRagAsawari(self):
                                           getNeighbor=Direction.DESCENDING)),
                          'F1')
 
-        self.assertEqual(str(sc.pitchFromDegree(1)), 'C1')
+        self.assertEqual(str(sc.pitchFromDegree(1)), 'C4')
         # there is no third step in ascending form
         self.assertEqual(str(sc.pitchFromDegree(3)), 'None')
         self.assertEqual(str(sc.pitchFromDegree(3, direction=Direction.DESCENDING)),