matplotlib · QuLogic · Sep 5, 2026 · Sep 5, 2026
diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
@@ -364,6 +364,12 @@ def __init__(self, default_font_prop: FontProperties, load_glyph_flags: LoadFlag
         self._fonts['default'] = default_font
         self._fonts['regular'] = default_font
 
+    def _normalize_font_pattern(self, pattern: str) -> str:
+        for option in ['stretch', 'style', 'variant', 'weight']:
+            if f':{option}=' not in pattern:
+                pattern = f'{pattern}:{option}=normal'
+        return pattern
+
     def _get_font(self, font: str) -> FT2Font:
         basename = self.fontmap.get(font, font)
         cached_font = self._fonts.get(basename)
@@ -492,7 +498,7 @@ def __init__(self, default_font_prop: FontProperties, load_glyph_flags: LoadFlag
 
         super().__init__(default_font_prop, load_glyph_flags)
         for key, val in self._fontmap.items():
-            fullpath = findfont(val)
+            fullpath = findfont(self._normalize_font_pattern(val))
             self.fontmap[key] = fullpath
             self.fontmap[val] = fullpath
 
@@ -617,7 +623,7 @@ def __init__(self, default_font_prop: FontProperties, load_glyph_flags: LoadFlag
             }
 
             for size, name in stixsizedaltfonts.items():
-                fullpath = findfont(name)
+                fullpath = findfont(self._normalize_font_pattern(name))
                 self.fontmap[size] = fullpath
                 self.fontmap[name] = fullpath
 
@@ -719,7 +725,7 @@ def __init__(self, default_font_prop: FontProperties, load_glyph_flags: LoadFlag
             '5': 'STIXSizeFiveSym',
         })
         for key, name in self._fontmap.items():
-            fullpath = findfont(name)
+            fullpath = findfont(self._normalize_font_pattern(name))
             self.fontmap[key] = fullpath
             self.fontmap[name] = fullpath
 
@@ -748,9 +754,9 @@ class DejaVuSerifFonts(DejaVuFonts):
     """
     _fontmap = {
         'rm': 'DejaVu Serif',
-        'it': 'DejaVu Serif:italic',
+        'it': 'DejaVu Serif:style=italic',
         'bf': 'DejaVu Serif:weight=bold',
-        'bfit': 'DejaVu Serif:italic:bold',
+        'bfit': 'DejaVu Serif:style=italic:weight=bold',
         'sf': 'DejaVu Sans',
         'tt': 'DejaVu Sans Mono',
         'ex': 'DejaVu Serif Display',
@@ -769,9 +775,9 @@ class DejaVuSansFonts(DejaVuFonts):
     """
     _fontmap = {
         'rm': 'DejaVu Sans',
-        'it': 'DejaVu Sans:italic',
+        'it': 'DejaVu Sans:style=italic',
         'bf': 'DejaVu Sans:weight=bold',
-        'bfit': 'DejaVu Sans:italic:bold',
+        'bfit': 'DejaVu Sans:style=italic:weight=bold',
         'sf': 'DejaVu Sans',
         'tt': 'DejaVu Sans Mono',
         'ex': 'DejaVu Sans Display',
@@ -796,11 +802,11 @@ class StixFonts(UnicodeFonts):
     """
     _fontmap = {
         'rm': 'STIXGeneral',
-        'it': 'STIXGeneral:italic',
+        'it': 'STIXGeneral:style=italic',
         'bf': 'STIXGeneral:weight=bold',
-        'bfit': 'STIXGeneral:italic:bold',
+        'bfit': 'STIXGeneral:style=italic:weight=bold',
         'nonunirm': 'STIXNonUnicode',
-        'nonuniit': 'STIXNonUnicode:italic',
+        'nonuniit': 'STIXNonUnicode:style=italic',
         'nonunibf': 'STIXNonUnicode:weight=bold',
         '0': 'STIXGeneral',
         '1': 'STIXSizeOneSym',
@@ -815,7 +821,7 @@ class StixFonts(UnicodeFonts):
     def __init__(self, default_font_prop: FontProperties, load_glyph_flags: LoadFlags):
         TruetypeFonts.__init__(self, default_font_prop, load_glyph_flags)
         for key, name in self._fontmap.items():
-            fullpath = findfont(name)
+            fullpath = findfont(self._normalize_font_pattern(name))
             self.fontmap[key] = fullpath
             self.fontmap[name] = fullpath
 

diff --git a/lib/matplotlib/tests/test_mathtext.py b/lib/matplotlib/tests/test_mathtext.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import io
+import logging
 from pathlib import Path
 import platform
 import re
@@ -292,14 +293,6 @@ def test_short_long_accents(fig_test, fig_ref):
         0, .5, "$" + "".join(fr"\{l} a" for l in corresponding_long_accs) + "$")
 
 
-def test_fontinfo():
-    fontpath = mpl.font_manager.findfont("DejaVu Sans")
-    font = mpl.ft2font.FT2Font(fontpath)
-    table = font.get_sfnt_table("head")
-    assert table is not None
-    assert table['version'] == (1, 0)
-
-
 # See gh-26152 for more context on this xfail
 @pytest.mark.xfail(pyparsing_version.release == (3, 1, 0),
                    reason="Error messages are incorrect for this version")
@@ -379,6 +372,35 @@ def test_mathtext_exceptions(math, msg):
         parser.parse(math)
 
 
+def test_mathtext_fonts(caplog):
+    # Changing these `font.*` rcParams should not affect mathtext, as that uses bundled
+    # fonts with a specific mapping to style/weight. TODO: font.stretch and font.variant
+    # are difficult to test as we don't have anything that might accidentally be
+    # substituted there.
+    mpl.rcParams['font.style'] = 'italic'
+    mpl.rcParams['font.weight'] = 100
+    # Use explicitly available default so that it doesn't warn.
+    default_font = fm.FontProperties('DejaVu Sans:style=normal:weight=normal')
+
+    _mathtext.BakomaFonts(default_font, LoadFlags.DEFAULT)
+    dejavusans = _mathtext.DejaVuSansFonts(default_font, LoadFlags.DEFAULT)
+    dejavuserif = _mathtext.DejaVuSerifFonts(default_font, LoadFlags.DEFAULT)
+    stix = _mathtext.StixFonts(default_font, LoadFlags.DEFAULT)
+    stixsans = _mathtext.StixSansFonts(default_font, LoadFlags.DEFAULT)
+
+    # Setting font.style should not have accidentally changed any roman font to italic.
+    assert dejavusans.fontmap['rm'].endswith('DejaVuSans.ttf')
+    assert dejavuserif.fontmap['rm'].endswith('DejaVuSerif.ttf')
+    assert stix.fontmap['rm'].endswith('STIXGeneral.ttf')
+    assert stixsans.fontmap['rm'].endswith('STIXGeneral.ttf')
+    # No bakoma font is actually italic, so that setting won't affect it.
+
+    # If `font.weight` leaked into the mathtext setup, then it should cause a warning to
+    # be logged from the font manager for a missing font weight.
+    records = [record for record in caplog.records if record.levelno == logging.WARNING]
+    assert records == []
+
+
 def test_get_unicode_index_exception():
     with pytest.raises(ValueError):
         _mathtext.get_unicode_index(r'\foo')