Extract shared plot label positioning into _position_plot_labels()

Deduplicate the title/subtitle/caption/footer positioning logic that
was nearly identical between PlotLayoutItems and CompositionLayoutItems.
Add boundary properties to PlotSideSpaces so both side-space classes
share the same interface. Remove no-op @DataClass from
CompositionLayoutItems.

Author: has2k1

plotnine/_mpl/layout_manager/_composition_layout_items.py

@@ -1,16 +1,10 @@
 from __future__ import annotations
 
-from dataclasses import dataclass
 from typing import TYPE_CHECKING
 
 from matplotlib.text import Text
 
-from plotnine._mpl.utils import (
-    ArtistGeometry,
-    TextJustifier,
-    resize_footer_background,
-    resize_footer_line,
-)
+from plotnine._mpl.utils import ArtistGeometry
 
 if TYPE_CHECKING:
     from typing import Any
@@ -23,7 +17,6 @@
     from ._composition_side_space import CompositionSideSpaces
 
 
-@dataclass
 class CompositionLayoutItems:
     """
     plot_annotation artists
@@ -61,61 +54,6 @@ def _move_artists(self, spaces: CompositionSideSpaces):
         """
         Move the annotations to their final positions
         """
-        theme = self.cmp.theme
-        plot_title_position = theme.getp("plot_title_position", "panel")
-        plot_caption_position = theme.getp("plot_caption_position", "panel")
-        plot_footer_position = theme.getp("plot_footer_position", "plot")
-        justify = TextJustifier.from_boundaries(
-            spaces.cmp.figure,
-            plot_left=spaces.plot_left,
-            plot_right=spaces.plot_right,
-            plot_bottom=spaces.plot_bottom,
-            plot_top=spaces.plot_top,
-            panel_left=spaces.panel_left,
-            panel_right=spaces.panel_right,
-            panel_bottom=spaces.panel_bottom,
-            panel_top=spaces.panel_top,
-        )
-
-        if self.plot_title:
-            ha = theme.getp(("plot_title", "ha"))
-            self.plot_title.set_y(spaces.t.y2("plot_title"))
-            justify.horizontally_about(
-                self.plot_title, ha, plot_title_position
-            )
-
-        if self.plot_subtitle:
-            ha = theme.getp(("plot_subtitle", "ha"))
-            self.plot_subtitle.set_y(spaces.t.y2("plot_subtitle"))
-            justify.horizontally_about(
-                self.plot_subtitle, ha, plot_title_position
-            )
-
-        if self.plot_caption:
-            ha = theme.getp(("plot_caption", "ha"), "right")
-            self.plot_caption.set_y(spaces.b.y1("plot_caption"))
-            justify.horizontally_about(
-                self.plot_caption, ha, plot_caption_position
-            )
+        from ._plot_layout_items import _position_plot_labels
 
-        if self.plot_footer:
-            ha = theme.getp(("plot_footer", "ha"), "left")
-            self.plot_footer.set_y(spaces.b.y1("plot_footer"))
-            justify.horizontally_about(
-                self.plot_footer, ha, plot_footer_position
-            )
-            if self.plot_footer_background:
-                resize_footer_background(
-                    self.plot_footer_background,
-                    x=spaces.l.offset,
-                    y=spaces.b.offset,
-                    height=spaces.b.footer_height,
-                    width=spaces.plot_width,
-                )
-            if self.plot_footer_line:
-                resize_footer_line(
-                    self.plot_footer_line,
-                    x=spaces.l.offset,
-                    width=spaces.plot_width,
-                    y=spaces.b.offset + spaces.b.footer_height,
-                )
+        _position_plot_labels(spaces.cmp.figure, self.cmp.theme, spaces, self)

plotnine/_mpl/layout_manager/_plot_layout_items.py

@@ -27,6 +27,7 @@
 
     from matplotlib.axes import Axes
     from matplotlib.axis import Tick
+    from matplotlib.figure import Figure
     from matplotlib.lines import Line2D
     from matplotlib.patches import Rectangle
     from matplotlib.transforms import Transform
@@ -36,10 +37,13 @@
     from plotnine._mpl.text import StripText
     from plotnine.iapi import legend_artists
     from plotnine.themes.elements import margin as Margin
+    from plotnine.themes.theme import theme
     from plotnine.typing import (
         StripPosition,
     )
 
+    from ._composition_layout_items import CompositionLayoutItems
+    from ._composition_side_space import CompositionSideSpaces
     from ._plot_side_space import PlotSideSpaces
 
     AxesLocation: TypeAlias = Literal[
@@ -352,67 +356,13 @@ def _move_artists(self, spaces: PlotSideSpaces):
         Move the artists to their final positions
         """
         theme = self.plot.theme
-        plot_title_position = theme.getp("plot_title_position", "panel")
-        plot_caption_position = theme.getp("plot_caption_position", "panel")
-        plot_footer_position = theme.getp("plot_footer_position", "plot")
-        justify = TextJustifier.from_boundaries(
-            spaces.plot.figure,
-            plot_left=spaces.l.plot_left,
-            plot_right=spaces.r.plot_right,
-            plot_bottom=spaces.b.plot_bottom,
-            plot_top=spaces.t.plot_top,
-            panel_left=spaces.l.panel_left,
-            panel_right=spaces.r.panel_right,
-            panel_bottom=spaces.b.panel_bottom,
-            panel_top=spaces.t.panel_top,
+        justify = _position_plot_labels(
+            spaces.plot.figure, theme, spaces, self
         )
 
         if self.plot_tag:
             set_plot_tag_position(self.plot_tag, spaces)
 
-        if self.plot_title:
-            ha = theme.getp(("plot_title", "ha"))
-            self.plot_title.set_y(spaces.t.y2("plot_title"))
-            justify.horizontally_about(
-                self.plot_title, ha, plot_title_position
-            )
-
-        if self.plot_subtitle:
-            ha = theme.getp(("plot_subtitle", "ha"))
-            self.plot_subtitle.set_y(spaces.t.y2("plot_subtitle"))
-            justify.horizontally_about(
-                self.plot_subtitle, ha, plot_title_position
-            )
-
-        if self.plot_caption:
-            ha = theme.getp(("plot_caption", "ha"), "right")
-            self.plot_caption.set_y(spaces.b.y1("plot_caption"))
-            justify.horizontally_about(
-                self.plot_caption, ha, plot_caption_position
-            )
-
-        if self.plot_footer:
-            ha = theme.getp(("plot_footer", "ha"), "left")
-            self.plot_footer.set_y(spaces.b.y1("plot_footer"))
-            justify.horizontally_about(
-                self.plot_footer, ha, plot_footer_position
-            )
-            if self.plot_footer_background:
-                resize_footer_background(
-                    self.plot_footer_background,
-                    x=spaces.l.offset,
-                    y=spaces.b.offset,
-                    height=spaces.b.footer_height,
-                    width=spaces.plot_width,
-                )
-            if self.plot_footer_line:
-                resize_footer_line(
-                    self.plot_footer_line,
-                    x=spaces.l.offset,
-                    width=spaces.plot_width,
-                    y=spaces.b.offset + spaces.b.footer_height,
-                )
-
         if self.axis_title_x:
             ha = theme.getp(("axis_title_x", "ha"), "center")
             self.axis_title_x.set_y(spaces.b.y1("axis_title_x"))
@@ -555,6 +505,75 @@ def _text_is_visible(text: Text) -> bool:
     return text.get_visible() and text._text  # type: ignore
 
 
+def _position_plot_labels(
+    figure: Figure,
+    theme: theme,
+    spaces: PlotSideSpaces | CompositionSideSpaces,
+    items: PlotLayoutItems | CompositionLayoutItems,
+) -> TextJustifier:
+    """
+    Position title, subtitle, caption, footer, and footer decorations
+
+    Returns the TextJustifier so the caller can reuse it for
+    additional positioning (e.g. axis titles).
+    """
+    plot_title_position = theme.getp("plot_title_position", "panel")
+    plot_caption_position = theme.getp("plot_caption_position", "panel")
+    plot_footer_position = theme.getp("plot_footer_position", "plot")
+    justify = TextJustifier.from_boundaries(
+        figure,
+        plot_left=spaces.plot_left,
+        plot_right=spaces.plot_right,
+        plot_bottom=spaces.plot_bottom,
+        plot_top=spaces.plot_top,
+        panel_left=spaces.panel_left,
+        panel_right=spaces.panel_right,
+        panel_bottom=spaces.panel_bottom,
+        panel_top=spaces.panel_top,
+    )
+
+    if items.plot_title:
+        ha = theme.getp(("plot_title", "ha"))
+        items.plot_title.set_y(spaces.t.y2("plot_title"))
+        justify.horizontally_about(items.plot_title, ha, plot_title_position)
+
+    if items.plot_subtitle:
+        ha = theme.getp(("plot_subtitle", "ha"))
+        items.plot_subtitle.set_y(spaces.t.y2("plot_subtitle"))
+        justify.horizontally_about(
+            items.plot_subtitle, ha, plot_title_position
+        )
+
+    if items.plot_caption:
+        ha = theme.getp(("plot_caption", "ha"), "right")
+        items.plot_caption.set_y(spaces.b.y1("plot_caption"))
+        justify.horizontally_about(
+            items.plot_caption, ha, plot_caption_position
+        )
+
+    if items.plot_footer:
+        ha = theme.getp(("plot_footer", "ha"), "left")
+        items.plot_footer.set_y(spaces.b.y1("plot_footer"))
+        justify.horizontally_about(items.plot_footer, ha, plot_footer_position)
+        if items.plot_footer_background:
+            resize_footer_background(
+                items.plot_footer_background,
+                x=spaces.l.offset,
+                y=spaces.b.offset,
+                height=spaces.b.footer_height,
+                width=spaces.plot_width,
+            )
+        if items.plot_footer_line:
+            resize_footer_line(
+                items.plot_footer_line,
+                x=spaces.l.offset,
+                width=spaces.plot_width,
+                y=spaces.b.offset + spaces.b.footer_height,
+            )
+
+    return justify
+
+
 def set_legends_position(legends: legend_artists, spaces: PlotSideSpaces):
     """
     Place legend on the figure and justify is a required

plotnine/_mpl/layout_manager/_plot_side_space.py

@@ -833,6 +833,38 @@ def panel_height(self) -> float:
         """
         return self.t.panel_top - self.b.panel_bottom
 
+    @property
+    def plot_left(self) -> float:
+        return self.l.plot_left
+
+    @property
+    def plot_right(self) -> float:
+        return self.r.plot_right
+
+    @property
+    def plot_bottom(self) -> float:
+        return self.b.plot_bottom
+
+    @property
+    def plot_top(self) -> float:
+        return self.t.plot_top
+
+    @property
+    def panel_left(self) -> float:
+        return self.l.panel_left
+
+    @property
+    def panel_right(self) -> float:
+        return self.r.panel_right
+
+    @property
+    def panel_bottom(self) -> float:
+        return self.b.panel_bottom
+
+    @property
+    def panel_top(self) -> float:
+        return self.t.panel_top
+
     @property
     def horizontal_space(self) -> float:
         """