gh-128067: Fix pyrepl overriding printed output without newlines

Lib/_pyrepl/unix_console.py

@@ -251,8 +251,9 @@ def refresh(self, screen, c_xy):
  if not self.__gone_tall:
  while len(self.screen) < min(len(screen), self.height):
  self.__hide_cursor()
- self.__move(0, len(self.screen) - 1)
- self.__write("\n")
+ if self.screen:
+ self.__move(0, len(self.screen) - 1)
+ self.__write("\n")
  self.posxy = 0, len(self.screen)
  self.screen.append("")
  else:
@@ -808,7 +809,7 @@ def __tputs(self, fmt, prog=delayprog):
  will never do anyone any good."""
  # using .get() means that things will blow up
  # only if the bps is actually needed (which I'm
- # betting is pretty unlkely)
+ # betting is pretty unlikely)
  bps = ratedict.get(self.__svtermstate.ospeed)
  while True:
  m = prog.search(fmt)

Lib/_pyrepl/windows_console.py

@@ -183,8 +183,9 @@ def refresh(self, screen: list[str], c_xy: tuple[int, int]) -> None:
 
  while len(self.screen) < min(len(screen), self.height):
  self._hide_cursor()
- self._move_relative(0, len(self.screen) - 1)
- self.__write("\n")
+ if self.screen:
+ self._move_relative(0, len(self.screen) - 1)
+ self.__write("\n")
  self.posxy = 0, len(self.screen)
  self.screen.append("")
 
@@ -501,7 +502,7 @@ def clear(self) -> None:
  """Wipe the screen"""
  self.__write(CLEAR)
  self.posxy = 0, 0
- self.screen = [""]
+ self.screen = []
 
  def finish(self) -> None:
  """Move the cursor to the end of the display and otherwise get

Lib/test/test_pyrepl/test_pyrepl.py

@@ -1829,6 +1829,44 @@ def test_detect_pip_usage_in_repl(self):
  )
  self.assertIn(hint, output)
 
+ @force_not_colorized
+ def test_no_newline(self):
+ env = os.environ.copy()
+ env.pop("PYTHON_BASIC_REPL", "")
+ env["PYTHON_BASIC_REPL"] = "1"
+
+ commands = "print('Something pretty long', end='')\nexit()\n"
+ expected_output_sequence = "Something pretty long>>> exit()"
+
+ basic_output, basic_exit_code = self.run_repl(commands, env=env)
+ self.assertEqual(basic_exit_code, 0)
+ self.assertIn(expected_output_sequence, basic_output)
+
+ output, exit_code = self.run_repl(commands)
+ self.assertEqual(exit_code, 0)
+
+ # Define escape sequences that don't affect cursor position or visual output
+ bracketed_paste_mode = r'\x1b\[\?2004[hl]' # Enable/disable bracketed paste
+ application_cursor_keys = r'\x1b\[\?1[hl]' # Enable/disable application cursor keys
+ application_keypad_mode = r'\x1b[=>]' # Enable/disable application keypad
+ insert_character = r'\x1b\[(?:1)?@(?=[ -~])' # Insert exactly 1 char (safe form)
+ cursor_visibility = r'\x1b\[\?25[hl]' # Show/hide cursor
+ cursor_blinking = r'\x1b\[\?12[hl]' # Start/stop cursor blinking
+ device_attributes = r'\x1b\[\?[01]c' # Device Attributes (DA) queries/responses
+
+ safe_escapes = re.compile(
+ f'{bracketed_paste_mode}|'
+ f'{application_cursor_keys}|'
+ f'{application_keypad_mode}|'
+ f'{insert_character}|'
+ f'{cursor_visibility}|'
+ f'{cursor_blinking}|'
+ f'{device_attributes}'
+ )
+ cleaned_output = safe_escapes.sub('', output)
+ self.assertIn(expected_output_sequence, cleaned_output)
+
+
 class TestPyReplCtrlD(TestCase):
  """Test Ctrl+D behavior in _pyrepl to match old pre-3.13 REPL behavior.
 

Lib/test/test_pyrepl/test_unix_console.py

@@ -102,6 +102,20 @@ def unix_console(events, **kwargs):
 @patch("os.write")
 @force_not_colorized_test_class
 class TestConsole(TestCase):
+ def test_no_newline(self, _os_write):
+ code = "1"
+ events = code_to_events(code)
+ _, con = handle_events_unix_console(events)
+ self.assertNotIn(call(ANY, b'\n'), _os_write.mock_calls)
+ con.restore()
+
+ def test_newline(self, _os_write):
+ code = "\n"
+ events = code_to_events(code)
+ _, con = handle_events_unix_console(events)
+ _os_write.assert_any_call(ANY, b"\n")
+ con.restore()
+
  def test_simple_addition(self, _os_write):
  code = "12+34"
  events = code_to_events(code)

Lib/test/test_pyrepl/test_windows_console.py

@@ -72,6 +72,20 @@ def handle_events_short(self, events, **kwargs):
  def handle_events_height_3(self, events):
  return self.handle_events(events, height=3)
 
+ def test_no_newline(self):
+ code = "1"
+ events = code_to_events(code)
+ _, con = self.handle_events(events)
+ self.assertNotIn(call(b'\n'), con.out.write.mock_calls)
+ con.restore()
+
+ def test_newline(self):
+ code = "\n"
+ events = code_to_events(code)
+ _, con = self.handle_events(events)
+ con.out.write.assert_any_call(b"\n")
+ con.restore()
+
  def test_simple_addition(self):
  code = "12+34"
  events = code_to_events(code)

Misc/ACKS

@@ -1349,6 +1349,7 @@ Gustavo Niemeyer
 Oscar Nierstrasz
 Lysandros Nikolaou
 Hrvoje Nikšić
+Jan-Eric Nitschke
 Gregory Nofi
 Jesse Noller
 Bill Noon

Misc/NEWS.d/next/Windows/2025-09-14-13-35-44.gh-issue-128067.BGdP_A.rst

@@ -0,0 +1 @@
+Fix a bug in PyREPL on Windows where output without a trailing newline was overwritten by the next prompt.