gh-128067: Fix pyrepl overriding printed output without newlines

[JanEricNitschke]

I tried a bit to debug this and narrowed it down to these two lines for windows and unix terminals respectively:

• https://github.com/python/cpython/blob/main/Lib/_pyrepl/windows_console.py#L186-L187
• https://github.com/python/cpython/blob/main/Lib/_pyrepl/unix_console.py#L238-L239

Because while properly running the repl in unix doesnt cause the issue, running the test i added also fails there before these changes.

I am not 100% sure if this is the base and 100% correct way, but it causes the test to pass on unix and fixes the issue on windows for me.

I also attempted to try to be able to run these tests for windows (because thats where we actually saw the issue) but didnt manage unfortunately.

With the fix in the unix console:

 python -m coverage run --pylib --branch --source=pyrepl Lib/test/regrtest.py  test_pyrepl -m test_no_newline
Using random seed: 4126788206
0:00:00 load avg: 0.17 Run 1 test sequentially in a single process
0:00:00 load avg: 0.17 [1/1] test_pyrepl
0:00:04 load avg: 0.17 [1/1] test_pyrepl passed

== Tests result: SUCCESS ==

1 test OK.

Total duration: 4.7 sec
Total tests: run=1 (filtered)
Total test files: run=1/1 (filtered)
Result: SUCCESS

Without:

 python -m coverage run --pylib --branch --source=pyrepl Lib/test/regrtest.py  test_pyrepl -m test_no_newline
Using random seed: 3832564122
0:00:00 load avg: 0.30 Run 1 test sequentially in a single process
0:00:00 load avg: 0.30 [1/1] test_pyrepl
test test_pyrepl failed -- Traceback (most recent call last):
  File "/mnt/d/Programming/Projects/cpython/Lib/test/support/__init__.py", line 2923, in wrapper
    return func(*args, **kwargs)
  File "/mnt/d/Programming/Projects/cpython/Lib/test/test_pyrepl/test_pyrepl.py", line 1819, in test_no_newline
    self.assertIn(expected_output_sequence, cleaned_output)
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 'Something pretty long>>> exit()' not found in 'print(\'Something pretty long\', end=\'\')\r\nexit()\r\nPython 3.15.0a0 (heads/main:c919d02ede, Sep  6 2025, 15:55:27) [GCC 13.3.0] on linux\r\nType "help", "copyright", "credits" or "license" for more information.\r\n\x1b[1A\n>>> print(\'Something pretty long\', end=\'\')\x1b[42D\n\rSomething pretty long\x1b[1A\n>>> exit()\x1b[10D\n\r'

0:00:02 load avg: 0.30 [1/1/1] test_pyrepl failed (1 failure)

== Tests result: FAILURE ==

1 test failed:
    test_pyrepl

Total duration: 2.0 sec
Total tests: run=1 (filtered) failures=1
Total test files: run=1/1 (filtered) failed=1
Result: FAILURE

• Issue: [Windows] Python 3.13 New REPL prompt swallows characters with print(..., end=" ") #128067

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[chris-eibl]

As written in the issue, this works fine on

• Windows 10 (in a legacy console and the new Windows terminal )
• WSL Ubuntu-24.04 (again in a legacy console and the new Windows terminal)
• native Ubuntu 24.0.4.3 LTS

[chris-eibl]

Spot on, len(self.screen) - 1 should not get negative here.

[chris-eibl]

Please add a News entry, see Quick reference #8 in the devguide.

[chris-eibl]

Please merge with latest default, because the pyrepl Windows tests are not run otherwise (#138801).

[JanEricNitschke]

Please merge with latest default, because the pyrepl Windows tests are not run otherwise (#138801).

So merge with current main and "merge" not "rebase", right? So basically just clicking the "Update branch" button here.

[chris-eibl]

I suggest to add tests like

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()

in test_unix_console.py and test_windows_console.py. Otherwise, for Windows we won't have any test coverage.

I think they are best placed before test_simple_addition?

Both tests fail before the PR and succeed with the PR.

So these tests might be enough, but of course your current test is more explict. But since Windows doesn't have the pty (Pseudo-terminal utilities), I don't know how to do a similar test there.

The filtering of the many escape sequences might induce some maintenance burden, but I don't think it is a big issue.

[chris-eibl]

Please merge with latest default, because the pyrepl Windows tests are not run otherwise (#138801).

So merge with current main and "merge" not "rebase", right? So basically just clicking the "Update branch" button here.

Correct. For reviewers it is easier to follow without squashing.

For the final merge from your fork to the upstream branch, squashing is used, anyway.

[JanEricNitschke]

Added the tests. I put the news entry under Windows because the main user visible effect here is on windows, although we did make changes to both unix and windows consoles.

[chris-eibl]

LGTM. Thank you @JanEricNitschke.

[chris-eibl]

I just found out, that in clear we can now change from

cpython/Lib/_pyrepl/windows_console.py

Line 517 in 8b5ce31

self.screen = [""]

to

cpython/Lib/_pyrepl/unix_console.py

Line 562 in 1c984ba

self.screen = []

like in unix_console.py (and like it is initialized in prepare in both implementations).

[JanEricNitschke]

Changed this for the windows console to be the same as for the unix one.

[JanEricNitschke]

Added myself to ACKS after the review/approval, hope thats alright.