support adding slide_layout

src/pptx/oxml/slide.py

@@ -258,6 +258,31 @@ class CT_SlideLayout(_BaseSlideElement):
     cSld: CT_CommonSlideData = OneAndOnlyOne("p:cSld")  # pyright: ignore[reportAssignmentType]
     del _tag_seq
 
+    @classmethod
+    def new(cls) -> CT_SlideLayout:
+        """Return new `p:sldLayout` element configured as base slide shape."""
+        return cast(CT_SlideLayout, parse_xml(cls._sld_xml()))
+
+    @staticmethod
+    def _sld_xml():
+        return (
+            "<p:sldLayout %s>\n"
+            "  <p:cSld>\n"
+            "    <p:spTree>\n"
+            "      <p:nvGrpSpPr>\n"
+            '        <p:cNvPr id="1" name=""/>\n'
+            "        <p:cNvGrpSpPr/>\n"
+            "        <p:nvPr/>\n"
+            "      </p:nvGrpSpPr>\n"
+            "      <p:grpSpPr/>\n"
+            "    </p:spTree>\n"
+            "  </p:cSld>\n"
+            "  <p:clrMapOvr>\n"
+            "    <a:masterClrMapping/>\n"
+            "  </p:clrMapOvr>\n"
+            "</p:sldLayout>" % nsdecls("a", "r", "p")
+        )
+
 
 class CT_SlideLayoutIdList(BaseOxmlElement):
     """`p:sldLayoutIdLst` element, child of `p:sldMaster`.
@@ -267,8 +292,43 @@ class CT_SlideLayoutIdList(BaseOxmlElement):
 
     sldLayoutId_lst: list[CT_SlideLayoutIdListEntry]
 
+    _add_sldLayoutId: Callable[..., CT_SlideLayoutIdListEntry]
     sldLayoutId = ZeroOrMore("p:sldLayoutId")
 
+    def add_sldLayoutId(self, rId: str) -> CT_SlideLayoutIdListEntry:
+        """Create and return a reference to a new `p:sldLayoutId` child element.
+
+        The new `p:sldLayoutId` element has its r:id attribute set to `rId`.
+        """
+        return self._add_sldLayoutId(id=self._next_id, rId=rId)
+
+    @property
+    def _next_id(self) -> int:
+        """The next available layout ID as an `int`.
+
+        Valid layout IDs start at 256. The next integer value greater than the max value in use is
+        chosen, which minimizes that chance of reusing the id of a deleted slide.
+        """
+        MIN_SLIDE_LAYOUT_ID = 256
+        MAX_SLIDE_LAYOUT_ID = 2147483647
+
+        used_ids = [int(s) for s in cast("list[str]", self.xpath("./p:sldLayoutId/@id"))]
+        simple_next = max([MIN_SLIDE_LAYOUT_ID - 1] + used_ids) + 1
+        if simple_next <= MAX_SLIDE_LAYOUT_ID:
+            return simple_next
+
+        # -- fall back to search for next unused from bottom --
+        valid_used_ids = sorted(id for id in used_ids if (MIN_SLIDE_LAYOUT_ID <= id <= MAX_SLIDE_LAYOUT_ID))
+        return (
+            next(
+                candidate_id
+                for candidate_id, used_id in enumerate(valid_used_ids, start=MIN_SLIDE_LAYOUT_ID)
+                if candidate_id != used_id
+            )
+            if valid_used_ids
+            else 256
+        )
+
 
 class CT_SlideLayoutIdListEntry(BaseOxmlElement):
     """`p:sldLayoutId` element, child of `p:sldLayoutIdLst`.

src/pptx/parts/slide.py

@@ -9,7 +9,7 @@
 from pptx.opc.constants import RELATIONSHIP_TYPE as RT
 from pptx.opc.package import XmlPart
 from pptx.opc.packuri import PackURI
-from pptx.oxml.slide import CT_NotesMaster, CT_NotesSlide, CT_Slide
+from pptx.oxml.slide import CT_NotesMaster, CT_NotesSlide, CT_Slide, CT_SlideLayout
 from pptx.oxml.theme import CT_OfficeStyleSheet
 from pptx.parts.chart import ChartPart
 from pptx.parts.embeddedpackage import EmbeddedPackagePart
@@ -266,6 +266,15 @@ class SlideLayoutPart(BaseSlidePart):
     Corresponds to package files ``ppt/slideLayouts/slideLayout[1-9][0-9]*.xml``.
     """
 
+    @classmethod
+    def new(cls, partname, package):
+        """Return newly-created blank slide layout part.
+
+        The new slide-part has `partname` and a relationship to `slide_layout_part`.
+        """
+        slide_layout_part = cls(partname, CT.PML_SLIDE_LAYOUT, package, CT_SlideLayout.new())
+        return slide_layout_part
+
     @lazyproperty
     def slide_layout(self):
         """
@@ -285,6 +294,16 @@ class SlideMasterPart(BaseSlidePart):
     Corresponds to package files ppt/slideMasters/slideMaster[1-9][0-9]*.xml.
     """
 
+    def add_layout(self):
+        """
+        Return (rId, layout) pair of a newly created layout.
+        """
+        partname = self._next_slideLayout_partname
+        slide_layout_part = SlideLayoutPart.new(partname, self.package)
+        rId = self.relate_to(slide_layout_part, RT.SLIDE_LAYOUT)
+        slide_layout_part.relate_to(self.slide_master.part, RT.SLIDE_MASTER)
+        return rId, slide_layout_part.slide_layout
+
     def related_slide_layout(self, rId: str) -> SlideLayout:
         """Return |SlideLayout| related to this slide-master by key `rId`."""
         return self.related_part(rId).slide_layout
@@ -295,3 +314,10 @@ def slide_master(self):
         The |SlideMaster| object representing this part.
         """
         return SlideMaster(self._element, self)
+
+    @property
+    def _next_slideLayout_partname(self):
+        """Return |PackURI| instance containing next available slideLayout partname."""
+        sldLayoutIdLst = self._element.get_or_add_sldLayoutIdLst()
+        partname_str = "/ppt/slideLayouts/slideLayout%d.xml" % (len(sldLayoutIdLst) + 1)
+        return PackURI(partname_str)

src/pptx/shapes/shapetree.py

@@ -648,13 +648,27 @@ def _shape_factory(self, shape_elm: ShapeElement) -> BaseShape:
         return SlideShapeFactory(shape_elm, self)
 
 
-class LayoutShapes(_BaseShapes):
+class LayoutShapes(_BaseGroupShapes):
     """Sequence of shapes appearing on a slide layout.
 
     The first shape in the sequence is the backmost in z-order and the last shape is topmost.
     Supports indexed access, len(), index(), and iteration.
     """
 
+    def add_placeholder(
+        self, ph_type: PP_PLACEHOLDER, orient: str, sz: str
+    ) -> LayoutPlaceholder:
+        """Return newly added placeholder appended to this shape tree.
+
+        The placeholder having the specified properties
+        """
+        id_ = self._next_shape_id
+        ph_name = self._next_ph_name(ph_type, id_, orient)
+        sp = self._spTree.add_placeholder(id_, ph_name, ph_type, orient, sz, id_)
+        sp = cast(LayoutPlaceholder, self._shape_factory(sp))
+
+        return sp
+
     def _shape_factory(self, shape_elm: ShapeElement) -> BaseShape:
         """Return an instance of the appropriate shape proxy class for `shape_elm`."""
         return _LayoutShapeFactory(shape_elm, self)

src/pptx/slide.py

@@ -370,6 +370,15 @@ def __len__(self) -> int:
         """Support len() built-in function, e.g. `len(slides) == 4`."""
         return len(self._sldLayoutIdLst)
 
+    def add_layout(self, name: str | None = "Layout %s") -> SlideLayout:
+        """Return a newly added slide layout."""
+        rId, layout = self.part.add_layout()
+        self._sldLayoutIdLst.add_sldLayoutId(rId)
+        id_ = int(rId[3:]) if rId.startswith("rId") and rId[3:].isdigit() else 0
+        if name:
+            layout.name = name % id_ if "%s" in name else name
+        return layout
+
     def get_by_name(self, name: str, default: SlideLayout | None = None) -> SlideLayout | None:
         """Return SlideLayout object having `name`, or `default` if not found."""
         for slide_layout in self: