Deprecate public access to XMLWriter; simplify some attribute settings.

anntzer · anntzer · commit 04fecdd1c09c · 2026-03-09T20:52:11.000+01:00
diff --git a/doc/api/next_api_changes/deprecations/31143-AL.rst b/doc/api/next_api_changes/deprecations/31143-AL.rst
@@ -0,0 +1,3 @@
+``backend_svg.XMLWriter`` is deprecated
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It is an internal helper not intended for external use.
diff --git a/lib/matplotlib/backends/backend_svg.py b/lib/matplotlib/backends/backend_svg.py
@@ -104,7 +104,7 @@ def _short_float_fmt(x):
     return f'{x:f}'.rstrip('0').rstrip('.')
 
 
-class XMLWriter:
+class _XMLWriter:
     """
     Parameters
     ----------
@@ -252,6 +252,15 @@ def flush(self):
         pass  # replaced by the constructor
 
 
+@mpl._api.deprecated("3.11")
+class XMLWriter(_XMLWriter):
+    """
+    An XML writer class.
+
+    :meta private:
+    """
+
+
 def _generate_transform(transform_list):
     parts = []
     for type, value in transform_list:
@@ -295,7 +304,7 @@ def __init__(self, width, height, svgwriter, basename=None, image_dpi=72,
                  *, metadata=None):
         self.width = width
         self.height = height
-        self.writer = XMLWriter(svgwriter)
+        self.writer = _XMLWriter(svgwriter)
         self.image_dpi = image_dpi  # actual dpi at which we rasterize stuff
 
         if basename is None:
@@ -926,7 +935,7 @@ def draw_gouraud_triangles(self, gc, triangles_array, colors_array,
                 id='colorMat')
             writer.element(
                 'feColorMatrix',
-                attrib={'type': 'matrix'},
+                type='matrix',
                 values='1 0 0 0 0 \n0 1 0 0 0 \n0 0 1 0 0 \n1 1 1 1 0 \n0 0 0 0 1 ')
             writer.end('filter')
 
@@ -982,37 +991,30 @@ def draw_image(self, gc, x, y, im, transform=None):
         if transform is None:
             w = 72.0 * w / self.image_dpi
             h = 72.0 * h / self.image_dpi
-
             self.writer.element(
                 'image',
                 transform=_generate_transform([
                     ('scale', (1, -1)), ('translate', (0, -h))]),
                 x=_short_float_fmt(x),
                 y=_short_float_fmt(-(self.height - y - h)),
                 width=_short_float_fmt(w), height=_short_float_fmt(h),
-                attrib=attrib)
+                attrib=attrib,
+            )
         else:
             alpha = gc.get_alpha()
             if alpha != 1.0:
                 attrib['opacity'] = _short_float_fmt(alpha)
-
             flipped = (
-                Affine2D().scale(1.0 / w, 1.0 / h) +
-                transform +
-                Affine2D()
-                .translate(x, y)
-                .scale(1.0, -1.0)
-                .translate(0.0, self.height))
-
-            attrib['transform'] = _generate_transform(
-                [('matrix', flipped.frozen())])
-            attrib['style'] = (
-                'image-rendering:crisp-edges;'
-                'image-rendering:pixelated')
+                Affine2D().scale(1 / w, 1 / h)
+                + transform
+                + Affine2D().translate(x, y).scale(1, -1).translate(0, self.height))
             self.writer.element(
                 'image',
                 width=_short_float_fmt(w), height=_short_float_fmt(h),
-                attrib=attrib)
+                attrib=attrib,
+                transform=_generate_transform([('matrix', flipped.frozen())]),
+                style='image-rendering:crisp-edges;image-rendering:pixelated',
+            )
 
         if url is not None:
             self.writer.end('a')
@@ -1060,14 +1062,15 @@ def _draw_text_as_path(self, gc, x, y, s, prop, angle, ismath, mtext=None):
         if alpha != 1:
             style['opacity'] = _short_float_fmt(alpha)
         font_scale = fontsize / text2path.FONT_SCALE
-        attrib = {
-            'style': _generate_css(style),
-            'transform': _generate_transform([
+        writer.start(
+            'g',
+            style=_generate_css(style),
+            transform=_generate_transform([
                 ('translate', (x, y)),
                 ('rotate', (-angle,)),
-                ('scale', (font_scale, -font_scale))]),
-        }
-        writer.start('g', attrib=attrib)
+                ('scale', (font_scale, -font_scale)),
+            ]),
+        )
 
         if not ismath:
             font = text2path._get_font(prop)

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	+``backend_svg.XMLWriter`` is deprecated
	`2`	`+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`
	`3`	`+It is an internal helper not intended for external use.`