Jan 28, 2026 · Jan 28, 2026 · Jan 28, 2026 · Jan 28, 2026
diff --git a/Lib/_pyrepl/windows_console.py b/Lib/_pyrepl/windows_console.py

        self.__write(newline[x_pos:])
        if wlen(newline) == self.width:
            # If we wrapped we want to start at the next line
            self._move_relative(0, y + 1)
            self.posxy = 0, y + 1
            if self.__vt_support:
                info = CONSOLE_SCREEN_BUFFER_INFO()
                if not GetConsoleScreenBufferInfo(OutHandle, info):
                    raise WinError(GetLastError())
                win_y = int(info.dwCursorPosition.Y - info.srWindow.Top)
                expected = y - self.__offset
                if win_y == expected + 1:
                    # Terminal wrapped to next row.
                    self.posxy = 0, y + 1
                else:
                    # Terminal did not wrap; cursor stays at end-of-line.
                    self.posxy = self.width, y
            else:
                # If we wrapped we want to start at the next line
                self._move_relative(0, y + 1)
                self.posxy = 0, y + 1
        else:
            self.posxy = wlen(newline), y

diff --git a/Lib/test/test_pyrepl/test_pyrepl.py b/Lib/test/test_pyrepl/test_pyrepl.py
 import tempfile
 from pkgutil import ModuleInfo
 from unittest import TestCase, skipUnless, skipIf, SkipTest
 from unittest.mock import patch
 from unittest.mock importMock,patch
 from test.support import force_not_colorized, make_clean_env, Py_DEBUG
 from test.support import has_subprocess_support, SHORT_TIMEOUT, STDLIB_DIR
 from test.support.import_helper import import_module
        )
        reader, _ = handle_all_events(events)
        self.assertEqual("hello", "".join(reader.buffer))


 @skipUnless(sys.platform == "win32", "Windows console VT behavior only")
 class TestWindowsConsoleVtEolWrap(TestCase):
    """
    When a line exactly fills the terminal width, VT terminals differ on whether
    the cursor immediately wraps to the next row. In VT mode we must synchronize
    our logical cursor position with the real console cursor.
    """
    def _make_console_like(self, *, width: int, offset: int, vt: bool):
        from _pyrepl import windows_console as wc

        con = object.__new__(wc.WindowsConsole)

        # Minimal state needed by __write_changed_line()
        con.width = width
        con.screen = []
        con.posxy = (0, 0)
        setattr(con, "_WindowsConsole__offset", offset)
        setattr(con, "_WindowsConsole__vt_support", vt)

        # Stub out side-effecting methods used by __write_changed_line()
        con._hide_cursor = Mock()
        con._erase_to_end = Mock()
        con._move_relative = Mock()
        con.move_cursor = Mock()
        setattr(con, "_WindowsConsole__write", Mock())

        return con, wc

    def test_vt_exact_width_line_did_wrap(self):
        # Terminal wrapped to next row: posxy should become (0, y+1).
        width = 10
        y = 3
        con, wc = self._make_console_like(width=width, offset=0, vt=True)

        def fake_gcsbi(_h, info):
            info.dwCursorPosition.X = 0
            # Visible window top = 0, cursor now on next visible row
            info.srWindow.Top = 0
            info.dwCursorPosition.Y = y + 1
            return True

        with patch.object(wc, "GetConsoleScreenBufferInfo", side_effect=fake_gcsbi), \
            patch.object(wc, "OutHandle", 1):
            old = ""
            new = "a" * width
            wc.WindowsConsole._WindowsConsole__write_changed_line(con, y, old, new, 0)
        self.assertEqual(con.posxy, (0, y + 1))
        self.assertNotIn((0, y + 1), [c.args for c in con._move_relative.mock_calls])

    def test_vt_exact_width_line_did_not_wrap(self):
        # Terminal did NOT wrap yet: posxy should stay at (width, y).
        width = 10
        y = 3
        con, wc = self._make_console_like(width=width, offset=0, vt=True)

        def fake_gcsbi(_h, info):
            info.dwCursorPosition.X = width
            info.srWindow.Top = 0
            # Cursor remains on the same visible row
            info.dwCursorPosition.Y = y
            return True

        with patch.object(wc, "GetConsoleScreenBufferInfo", side_effect=fake_gcsbi), \
            patch.object(wc, "OutHandle", 1):
            old = ""
            new = "a" * width
            wc.WindowsConsole._WindowsConsole__write_changed_line(con, y, old, new, 0)

        self.assertEqual(con.posxy, (width, y))
        self.assertNotIn((0, y + 1), [c.args for c in con._move_relative.mock_calls])
diff --git a/Misc/NEWS.d/next/Library/2026-01-28-06-50-37.gh-issue-144259.Xslknn.rst b/Misc/NEWS.d/next/Library/2026-01-28-06-50-37.gh-issue-144259.Xslknn.rst
 Fix Windows VT REPL cursor desynchronization when a line exactly fills the terminal width.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -272,9 +272,22 @@ def __write_changed_line(

		self.__write(newline[x_pos:])
		if wlen(newline) == self.width:
		# If we wrapped we want to start at the next line
		self._move_relative(0, y + 1)
		self.posxy = 0, y + 1
		if self.__vt_support:
		info = CONSOLE_SCREEN_BUFFER_INFO()
		if not GetConsoleScreenBufferInfo(OutHandle, info):
		raise WinError(GetLastError())
		win_y = int(info.dwCursorPosition.Y - info.srWindow.Top)
		expected = y - self.__offset
		if win_y == expected + 1:
		# Terminal wrapped to next row.
		self.posxy = 0, y + 1
		else:
		# Terminal did not wrap; cursor stays at end-of-line.
		self.posxy = self.width, y
		else:
		# If we wrapped we want to start at the next line
		self._move_relative(0, y + 1)
		self.posxy = 0, y + 1
		else:
		self.posxy = wlen(newline), y

Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -12,7 +12,7 @@
		import tempfile
		from pkgutil import ModuleInfo
		from unittest import TestCase, skipUnless, skipIf, SkipTest
		from unittest.mock import patch
		from unittest.mock importMock,patch
		from test.support import force_not_colorized, make_clean_env, Py_DEBUG
		from test.support import has_subprocess_support, SHORT_TIMEOUT, STDLIB_DIR
		from test.support.import_helper import import_module
Expand DownExpand Up		@@ -2105,3 +2105,75 @@ def test_ctrl_d_single_line_end_no_newline(self):
		)
		reader, _ = handle_all_events(events)
		self.assertEqual("hello", "".join(reader.buffer))


		@skipUnless(sys.platform == "win32", "Windows console VT behavior only")
		class TestWindowsConsoleVtEolWrap(TestCase):
		"""
		When a line exactly fills the terminal width, VT terminals differ on whether
		the cursor immediately wraps to the next row. In VT mode we must synchronize
		our logical cursor position with the real console cursor.
		"""
		def _make_console_like(self, *, width: int, offset: int, vt: bool):
		from _pyrepl import windows_console as wc

		con = object.__new__(wc.WindowsConsole)

		# Minimal state needed by __write_changed_line()
		con.width = width
		con.screen = []
		con.posxy = (0, 0)
		setattr(con, "_WindowsConsole__offset", offset)
		setattr(con, "_WindowsConsole__vt_support", vt)

		# Stub out side-effecting methods used by __write_changed_line()
		con._hide_cursor = Mock()
		con._erase_to_end = Mock()
		con._move_relative = Mock()
		con.move_cursor = Mock()
		setattr(con, "_WindowsConsole__write", Mock())

		return con, wc

		def test_vt_exact_width_line_did_wrap(self):
		# Terminal wrapped to next row: posxy should become (0, y+1).
		width = 10
		y = 3
		con, wc = self._make_console_like(width=width, offset=0, vt=True)

		def fake_gcsbi(_h, info):
		info.dwCursorPosition.X = 0
		# Visible window top = 0, cursor now on next visible row
		info.srWindow.Top = 0
		info.dwCursorPosition.Y = y + 1
		return True

		with patch.object(wc, "GetConsoleScreenBufferInfo", side_effect=fake_gcsbi), \
		patch.object(wc, "OutHandle", 1):
		old = ""
		new = "a" * width
		wc.WindowsConsole._WindowsConsole__write_changed_line(con, y, old, new, 0)
		self.assertEqual(con.posxy, (0, y + 1))
		self.assertNotIn((0, y + 1), [c.args for c in con._move_relative.mock_calls])

		def test_vt_exact_width_line_did_not_wrap(self):
		# Terminal did NOT wrap yet: posxy should stay at (width, y).
		width = 10
		y = 3
		con, wc = self._make_console_like(width=width, offset=0, vt=True)

		def fake_gcsbi(_h, info):
		info.dwCursorPosition.X = width
		info.srWindow.Top = 0
		# Cursor remains on the same visible row
		info.dwCursorPosition.Y = y
		return True

		with patch.object(wc, "GetConsoleScreenBufferInfo", side_effect=fake_gcsbi), \
		patch.object(wc, "OutHandle", 1):
		old = ""
		new = "a" * width
		wc.WindowsConsole._WindowsConsole__write_changed_line(con, y, old, new, 0)

		self.assertEqual(con.posxy, (width, y))
		self.assertNotIn((0, y + 1), [c.args for c in con._move_relative.mock_calls])
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Fix Windows VT REPL cursor desynchronization when a line exactly fills the terminal width.