gh-156961: Fix tkinter.font.Font for a font name returned as a Tcl object

Lib/test/test_tkinter/test_font.py

@@ -24,6 +24,16 @@ def actual_size(self, desc):
         # The requested size is not always available (e.g. bitmap fonts).
         return self.root.tk.call('font', 'actual', desc, '-size')
 
+    def tcl_font_object(self, desc):
+        # Return a font name or description as a Tcl object representing a
+        # font, as Tk returns for example from ttk.Style().lookup().
+        tk = self.root.tk
+        tk.call('set', '_font', desc)
+        tk.eval('font measure $_font x')  # convert the Tcl object to a font
+        obj = tk.call('set', '_font')
+        tk.call('unset', '_font')
+        return obj
+
     def test_configure(self):
         self.assertEqual(self.font.config, self.font.configure)
         options = self.font.configure()
@@ -150,6 +160,36 @@ def test_existing(self):
         # A name or a description is required.
         self.assertRaises(TypeError, font.Font, root=self.root, exists=True)
 
+    def test_tcl_object(self):
+        # Tk can return a font as a Tcl object (gh-156961).
+        if not self.wantobjects:
+            self.skipTest('Tcl objects are converted to strings')
+        obj = self.tcl_font_object(fontname)
+        self.assertEqual(obj.typename, 'font')
+
+        # It can be used as the name of an existing named font.
+        for f in (font.Font(root=self.root, name=obj, exists=True),
+                  font.nametofont(obj, root=self.root)):
+            # The Tcl object is kept as is, so that it is passed back to Tk.
+            self.assertIs(f.name, obj)
+            self.assertEqual(str(f), fontname)
+            self.assertEqual(f.actual(), self.font.actual())
+            self.assertEqual(f, self.font)
+            self.assertEqual(self.font, f)
+        # Referring to a non-existent named font still fails.
+        self.assertRaisesRegex(tkinter.TclError, 'named font nosuchfont',
+                               font.Font, root=self.root, exists=True,
+                               name=self.tcl_font_object('nosuchfont'))
+
+        # It can also be wrapped as a font description.
+        obj = self.tcl_font_object(('Times', 20, 'bold'))
+        f = font.Font(root=self.root, font=obj, exists=True)
+        self.assertIs(f.name, obj)
+        self.assertEqual(str(f), 'Times 20 bold')
+        self.assertNotIn(f.name, font.names(self.root))
+        self.assertEqual(f.actual('weight'), 'bold')
+        self.assertEqual(f.actual('size'), self.actual_size(('Times', 20, 'bold')))
+
     def test_copy(self):
         # size=-20 (pixels): copy() copies the configured options, so the
         # size is preserved rather than resolved (gh-143990).

Lib/tkinter/font.py

@@ -104,7 +104,8 @@ def __init__(self, root=None, font=None, name=None, exists=False,
             if exists:
                 self.name = name
                 # confirm font exists
-                if self.name not in tk.splitlist(tk.call("font", "names")):
+                name = getattr(name, 'string', name)  # can be a Tcl object
+                if name not in tk.splitlist(tk.call("font", "names")):
                     raise tkinter._tkinter.TclError(
                         "named font %s does not already exist" % (self.name,))
                 # if font config info supplied, apply it
@@ -123,11 +124,11 @@ def __init__(self, root=None, font=None, name=None, exists=False,
         self._call  = tk.call
 
     def __str__(self):
-        # A wrapped description is a list or tuple, not a string; format it as
-        # a Tcl word so it can be used as an option value (as ttk does).
-        if isinstance(self.name, str):
-            return self.name
-        return tkinter._join(self.name)
+        # A wrapped description can be a list or tuple; format it as a Tcl
+        # word so it can be used as an option value (as ttk does).
+        if isinstance(self.name, (list, tuple)):
+            return tkinter._join(self.name)
+        return str(self.name)
 
     def __repr__(self):
         return f"<{self.__class__.__module__}.{self.__class__.__qualname__}" \
@@ -136,7 +137,13 @@ def __repr__(self):
     def __eq__(self, other):
         if not isinstance(other, Font):
             return NotImplemented
-        return self.name == other.name and self._tk == other._tk
+        name = self.name
+        other_name = other.name
+        if type(name) is not type(other_name):
+            # A Tcl object does not compare equal to a string.
+            name = getattr(name, 'string', name)
+            other_name = getattr(other_name, 'string', other_name)
+        return name == other_name and self._tk == other._tk
 
     def __getitem__(self, key):
         return self.cget(key)

Misc/NEWS.d/next/Library/2026-09-05-22-39-22.gh-issue-156961.ZtYqoA.rst

@@ -0,0 +1,3 @@
+Fix :func:`tkinter.font.nametofont` and the :class:`tkinter.font.Font`
+constructor for a font name or description returned by Tk as a Tcl object,
+for example by :meth:`ttk.Style.lookup() <tkinter.ttk.Style.lookup>`.