Inconsistent display of long multiline pasted content in the REPL

[GabrielvMarinho]

Bug report

Bug description:

Pasting multiline content with long lines (more columns than the current terminal width) causes an unusual behavior on the REPL display, this happens on cmd and powershell.

x = None
y = {"a": 1, "b": 2, "c": 3, "d": 4, "e": 5, "f": 6, "g": 7, "h": 8, "i": 9, "j": 10}

Pasting this snippet in the REPL will cause this:

The interpreter actually handles the content correctly, but the editing of this is weird and leads to confusion.

Video Example

issue_video.mp4

More info

I believe this issue is windows-only, as far as I have tested, this works perfectly on Ubuntu 22.
Python 3.13 didn't have this issue, while 3.14 introduced this and 3.15 still has it.

CPython versions tested on:

3.15

Operating systems tested on:

Windows

[hyongtao-code]

Hi, I'd like to take on this issue. Could you please assign it to me? Thanks!

[sergey-miryanov]

@hyongtao-code
We don't usually assign issues. If @GabrielvMarinho doesn't mind feel free to start working and open a PR.

[yihong0618]

the same as this and it is closing by my accident delete my fork, so some code can help here, if you'd like take it

#140502

#140697

[hyongtao-code]

This issue was introduced by commit fac41f5 and occurs on Windows when PYTHON_BASIC_REPL=0.

In Windows VT mode, the old code assumed an EOL wrap always happens, moved the cursor to the next line, and updated posxy accordingly. When the terminal did not actually wrap, the real cursor position diverged from the internal cursor state, causing display and paste misalignment.

The solution may be to synchronize with the real cursor position. I’ve proposed this fix for discussion; it may resolve the issue.

diff --git a/Lib/_pyrepl/windows_console.py b/Lib/_pyrepl/windows_console.py
index 303af8a354..c62c02f505 100644
--- a/Lib/_pyrepl/windows_console.py
+++ b/Lib/_pyrepl/windows_console.py
@@ -272,9 +272,23 @@ 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

[GabrielvMarinho]

Firstly, thank you @hyongtao-code for taking the time to take a look at this, I tested this on my machine and it seems to work just fine. Do you plan to open a pull request now?