fix: add notesMasterIdLst element when creating notes master

src/pptx/oxml/__init__.py

@@ -273,6 +273,8 @@ def register_element_cls(nsptagname: str, cls: Type[BaseOxmlElement]):
 
 
 from pptx.oxml.presentation import (  # noqa: E402
+    CT_NotesMasterIdList,
+    CT_NotesMasterIdListEntry,
     CT_Presentation,
     CT_SlideId,
     CT_SlideIdList,
@@ -281,6 +283,8 @@ def register_element_cls(nsptagname: str, cls: Type[BaseOxmlElement]):
     CT_SlideSize,
 )
 
+register_element_cls("p:notesMasterId", CT_NotesMasterIdListEntry)
+register_element_cls("p:notesMasterIdLst", CT_NotesMasterIdList)
 register_element_cls("p:presentation", CT_Presentation)
 register_element_cls("p:sldId", CT_SlideId)
 register_element_cls("p:sldIdLst", CT_SlideIdList)

src/pptx/oxml/presentation.py

@@ -17,6 +17,7 @@ class CT_Presentation(BaseOxmlElement):
     get_or_add_sldSz: Callable[[], CT_SlideSize]
     get_or_add_sldIdLst: Callable[[], CT_SlideIdList]
     get_or_add_sldMasterIdLst: Callable[[], CT_SlideMasterIdList]
+    get_or_add_notesMasterIdLst: Callable[[], CT_NotesMasterIdList]
 
     sldMasterIdLst: CT_SlideMasterIdList | None = (
         ZeroOrOne(  # pyright: ignore[reportAssignmentType]
@@ -30,6 +31,17 @@ class CT_Presentation(BaseOxmlElement):
             ),
         )
     )
+    notesMasterIdLst: CT_NotesMasterIdList | None = (
+        ZeroOrOne(  # pyright: ignore[reportAssignmentType]
+            "p:notesMasterIdLst",
+            successors=(
+                "p:handoutMasterIdLst",
+                "p:sldIdLst",
+                "p:sldSz",
+                "p:notesSz",
+            ),
+        )
+    )
     sldIdLst: CT_SlideIdList | None = ZeroOrOne(  # pyright: ignore[reportAssignmentType]
         "p:sldIdLst", successors=("p:sldSz", "p:notesSz")
     )
@@ -115,6 +127,30 @@ class CT_SlideMasterIdListEntry(BaseOxmlElement):
     rId: str = RequiredAttribute("r:id", XsdString)  # pyright: ignore[reportAssignmentType]
 
 
+class CT_NotesMasterIdList(BaseOxmlElement):
+    """`p:notesMasterIdLst` element.
+
+    Child of `p:presentation` containing a reference to the notes master that belongs to the
+    presentation.
+    """
+
+    _add_notesMasterId: Callable[..., CT_NotesMasterIdListEntry]
+    notesMasterId = ZeroOrOne("p:notesMasterId")
+
+    def add_notesMasterId(self, rId: str) -> CT_NotesMasterIdListEntry:
+        """Create and return a new `p:notesMasterId` child element with r:id set to `rId`."""
+        return self._add_notesMasterId(rId=rId)
+
+
+class CT_NotesMasterIdListEntry(BaseOxmlElement):
+    """`p:notesMasterId` element.
+
+    Child of `p:notesMasterIdLst` containing an `rId` reference to the notes master part.
+    """
+
+    rId: str = RequiredAttribute("r:id", XsdString)  # pyright: ignore[reportAssignmentType]
+
+
 class CT_SlideSize(BaseOxmlElement):
     """`p:sldSz` element.
 

src/pptx/parts/presentation.py

@@ -72,7 +72,8 @@ def notes_master_part(self) -> NotesMasterPart:
             return self.part_related_by(RT.NOTES_MASTER)
         except KeyError:
             notes_master_part = NotesMasterPart.create_default(self.package)
-            self.relate_to(notes_master_part, RT.NOTES_MASTER)
+            rId = self.relate_to(notes_master_part, RT.NOTES_MASTER)
+            self._element.get_or_add_notesMasterIdLst().add_notesMasterId(rId)
             return notes_master_part
 
     @lazyproperty

tests/parts/test_presentation.py

@@ -65,13 +65,21 @@ def but_it_adds_a_notes_master_part_when_needed(
         NotesMasterPart_ = class_mock(request, "pptx.parts.presentation.NotesMasterPart")
         NotesMasterPart_.create_default.return_value = notes_master_part_
         part_related_by_.side_effect = KeyError
-        prs_part = PresentationPart(None, None, package_, None)
+        relate_to_.return_value = "rId42"
+        prs_elm = element("p:presentation/p:sldMasterIdLst")
+        prs_part = PresentationPart(None, None, package_, prs_elm)
 
         notes_master_part = prs_part.notes_master_part
 
         NotesMasterPart_.create_default.assert_called_once_with(package_)
         relate_to_.assert_called_once_with(prs_part, notes_master_part_, RT.NOTES_MASTER)
         assert notes_master_part is notes_master_part_
+        # --- notesMasterIdLst element was added to presentation.xml ---
+        notesMasterIdLst = prs_elm.notesMasterIdLst
+        assert notesMasterIdLst is not None
+        notesMasterId = notesMasterIdLst.notesMasterId
+        assert notesMasterId is not None
+        assert notesMasterId.rId == "rId42"
 
     def it_provides_access_to_its_notes_master(self, request, notes_master_part_):
         notes_master_ = instance_mock(request, NotesMaster)