gh-151675: Add tkinter Text.sync() and Text.pendingsync()

Doc/library/tkinter.rst

@@ -5594,6 +5594,29 @@ Widget classes
 
       .. versionadded:: 3.3
 
+   .. method:: sync(command=None)
+
+      Control the synchronization of the displayed view with the underlying
+      text, which may lag behind when line heights have not yet been computed
+      (for example, for lines that have never been displayed).
+      If *command* is omitted, bring the line metrics up to date immediately by
+      forcing computation of any outdated line heights, and return once they
+      are current.
+      Otherwise schedule *command* to be called, with no arguments, exactly
+      once as soon as all line heights are up to date; if there are no pending
+      calculations, it is called immediately.
+
+      .. versionadded:: next
+
+   .. method:: pendingsync()
+
+      Return ``True`` if the line height calculations are not up to date, and
+      ``False`` otherwise.
+      The ``<<WidgetViewSync>>`` virtual event fires whenever this state
+      changes, with the *detail* field set to the new value.
+
+      .. versionadded:: next
+
    .. method:: yview_pickplace(*what)
 
       Adjust the view so that the location given by *what* is visible.

Doc/whatsnew/3.16.rst

@@ -144,6 +144,14 @@ shlex
   a string, even if it is already safe for a shell without being quoted.
   (Contributed by Jay Berry in :gh:`148846`.)
 
+tkinter
+-------
+
+* Added new :class:`!tkinter.Text` methods :meth:`~tkinter.Text.sync` and
+  :meth:`~tkinter.Text.pendingsync` which control and report the
+  synchronization of the displayed view with the underlying text.
+  (Contributed by Serhiy Storchaka in :gh:`151675`.)
+
 xml
 ---
 

Lib/test/test_tkinter/test_text.py

@@ -26,6 +26,18 @@ def test_debug(self):
             text.debug(olddebug)
             self.assertEqual(text.debug(), olddebug)
 
+    def test_sync(self):
+        text = self.text
+        # sync() returns None and brings line metrics up to date.
+        self.assertIsNone(text.sync())
+        self.assertIs(text.pendingsync(), False)
+
+        # sync(command) schedules a one-shot callback.
+        events = []
+        text.sync(command=lambda: events.append('synced'))
+        text.update()
+        self.assertEqual(events, ['synced'])
+
     def test_index(self):
         text = self.text
         text.insert('1.0', 'Lorem ipsum\ndolor sit amet')

Lib/tkinter/__init__.py

@@ -4094,6 +4094,44 @@ def peer_names(self): # new in Tk 8.5
         the widget itself)."""
         return self.tk.splitlist(self.tk.call(self._w, 'peer', 'names'))
 
+    def pendingsync(self): # new in Tk 8.5
+        """Return whether the line heights calculations are not up-to-date.
+
+        Return True if the line heights calculations are not up-to-date,
+        and False otherwise.
+        """
+        return self.tk.getboolean(self.tk.call(self._w, 'pendingsync'))
+
+    def sync(self, command=None): # new in Tk 8.5
+        """Control the synchronization of the view of the text widget.
+
+        If command is not specified, immediately bring the line metrics
+        up-to-date by forcing computation of any outdated line heights.
+        The command returns immediately if there is no such outdated line.
+
+        If command is specified, schedule it to be executed (by the event
+        loop) exactly once as soon as all line heights are up-to-date.
+        If there are no pending line metrics calculations, command is
+        executed immediately.
+        """
+        if command is None:
+            self.tk.call(self._w, 'sync')
+        else:
+            def callit():
+                try:
+                    command()
+                finally:
+                    try:
+                        self.deletecommand(name)
+                    except TclError:
+                        pass
+            try:
+                callit.__name__ = command.__name__
+            except AttributeError:
+                callit.__name__ = type(command).__name__
+            name = self._register(callit)
+            self.tk.call(self._w, 'sync', '-command', name)
+
     def replace(self, index1, index2, chars, *args): # new in Tk 8.5
         """Replaces the range of characters between index1 and index2 with
         the given characters and tags specified by args.

Misc/NEWS.d/next/Library/2026-06-19-12-00-01.gh-issue-151675.acLD7L.rst

@@ -0,0 +1,3 @@
+Add the :meth:`~tkinter.Text.sync` and :meth:`~tkinter.Text.pendingsync`
+methods of :class:`!tkinter.Text`, wrapping the Tk ``sync`` and
+``pendingsync`` subcommands.