matplotlib · ksunden · Jul 11, 2023 · Apr 11, 2023 · oscargus · Apr 11, 2023
diff --git a/doc/users/next_whats_new/boldsym_mathtext.rst b/doc/users/next_whats_new/boldsym_mathtext.rst
@@ -0,0 +1,14 @@
+Boldsymbol mathtext command ``\boldsymbol``
+-------------------------------------------
+
+Supports using the ``\boldsymbol{}`` command in mathtext:
+
+To change symbols to bold enclose the text in a font command as
+shown:
+
+.. code-block::
+
+    r'$\boldsymbol{a+2+\alpha}$'
+
+.. math::
+   \boldsymbol{a+2+\alpha}
diff --git a/lib/matplotlib/_mathtext.py b/lib/matplotlib/_mathtext.py
@@ -11,6 +11,7 @@
 import re
 import types
 import unicodedata
+import string
 
 import numpy as np
 from pyparsing import (
@@ -1811,6 +1812,11 @@ class _MathStyle(enum.Enum):
     _right_delims = set(r") ] \} > \rfloor \rangle \rceil".split())
     _delims = _left_delims | _right_delims | _ambi_delims
 
+    _small_greek = set([unicodedata.name(chr(i)).split()[-1].lower() for i in
+                       range(ord('\N{GREEK SMALL LETTER ALPHA}'),
+                             ord('\N{GREEK SMALL LETTER OMEGA}') + 1)])
+    _latin_alphabets = set(string.ascii_letters)
+
     def __init__(self):
         p = types.SimpleNamespace()
 
@@ -1933,6 +1939,9 @@ def csnames(group, names):
 
         p.operatorname = cmd(r"\operatorname", "{" + ZeroOrMore(p.simple)("name") + "}")
 
+        p.boldsymbol = cmd(
+            r"\boldsymbol", "{" + ZeroOrMore(p.simple)("value") + "}")
+
         p.placeable     <<= (
             p.accent     # Must be before symbol as all accents are symbols
             | p.symbol   # Must be second to catch all named symbols and single
@@ -1949,6 +1958,7 @@ def csnames(group, names):
             | p.sqrt
             | p.overline
             | p.text
+            | p.boldsymbol
         )
 
         p.auto_delim    <<= (
@@ -2597,3 +2607,29 @@ def auto_delim(self, s, loc, toks):
             # if "mid" in toks ... can be removed when requiring pyparsing 3.
             toks["mid"].asList() if "mid" in toks else [],
             toks["right"])
+
+    def boldsymbol(self, s, loc, toks):
+        self.push_state()
+        state = self.get_state()
+        hlist = []
+        name = toks["value"]
+        for c in name:
+            if isinstance(c, Hlist):
+                k = c.children[1]
+                if isinstance(k, Char):
+                    k.font = "bf"
+                    k._update_metrics()
+                hlist.append(c)
+            elif isinstance(c, Char):
+                c.font = "bf"
+                if (c.c in self._latin_alphabets or
+                   c.c[1:] in self._small_greek):
+                    c.font = "bfit"
+                    c._update_metrics()
+                c._update_metrics()
+                hlist.append(c)
+            else:
+                hlist.append(c)
+        self.pop_state()
+
+        return Hlist(hlist)
diff --git a/lib/matplotlib/tests/baseline_images/test_mathtext/mathtext1_dejavusans_05.png b/lib/matplotlib/tests/baseline_images/test_mathtext/mathtext1_dejavusans_05.png
diff --git a/lib/matplotlib/tests/test_mathtext.py b/lib/matplotlib/tests/test_mathtext.py
@@ -134,7 +134,7 @@
     r'$\sum x\quad\sum^nx\quad\sum_nx\quad\sum_n^nx\quad\prod x\quad\prod^nx\quad\prod_nx\quad\prod_n^nx$',  # GitHub issue 18085
     r'$1.$ $2.$ $19680801.$ $a.$ $b.$ $mpl.$',
     r'$\text{text}_{\text{sub}}^{\text{sup}} + \text{\$foo\$} + \frac{\text{num}}{\mathbf{\text{den}}}\text{with space, curly brackets \{\}, and dash -}$',
-
+    r'$\boldsymbol{abcde} \boldsymbol{+} \boldsymbol{\Gamma + \Omega} \boldsymbol{01234} \boldsymbol{\alpha * \beta}$',
 ]
 
 digits = "0123456789"
@@ -538,3 +538,9 @@ def test_mathtext_operators():
         fig.text(0.5, (x + 0.5)/len(test_str), r'${%s}$' % i)
 
     fig.draw_without_rendering()
+
+
+@check_figures_equal(extensions=["png"])
+def test_boldsymbol(fig_test, fig_ref):
+    fig_test.text(0.1, 0.2, r"$\boldsymbol{\mathrm{abc0123\alpha}}$")
+    fig_ref.text(0.1, 0.2, r"$\mathrm{abc0123\alpha}$")