high CPU usage and freezing in Python REPL with half space character (U+200C)

[houshmand-2005]

Bug report

Bug description:

When entering comments in Python's REPL that contain a Half Space character (U+200C) the REPL experiences 100% CPU usage and becomes unresponsive (freezes) when using the up arrow to retrieve previous code line

• https://unicode-explorer.com/c/200C

Steps to Reproduce:

1. Go to Python REPL
2. Paste the following lines (for Windows, use F3 to activate paste mode):

# Half space ‌text
# Up arrow key

3. Press the up arrow key to navigate back to the previous line (# Half space ‌text)

(If it doesn't work for you, go to the end of the line # Up arrow key and press the up button. It should freeze now. You can use Ctrl+C to interrupt the program, which resolves the freeze.)

---

in terminal this looks like this:

>>> # Half space \u200ctext
... # Up arrow key

This problem also exists in Windows when using F3 (to active the paste mode):

In Linux no need to active paste mode:

I can't check if this problem exists on previous python version because they break each line so i cant use up arrow to go to the previous line.

Half Space character is often used in Persian and I think in other languages that utilize right-to-left . It helps in adjusting the spacing between characters for better readability

---

Also a small note: when I use the half space at the end and no text after it, there is no problem:

# Half space ‌
# Up arrow key

in terminal:

>>> # Half space \u200c
... # Up arrow key

System Information:

• Linux: Python 3.13.0rc2 | Fedora 40
• Windows Python 3.13.0rc3 | Windows 11

CPython versions tested on:

3.13

Operating systems tested on:

Linux, Windows

Linked PRs

• gh-124927: Fix conversion issue between coordinates and position in REPL #125001

[qqwqqw689]

My python versoin is 3.11.5. It seems nothing happen in win10.

[skirpichev]

My python versoin is 3.11.5. It seems nothing happen in win10.

Then you, probably, use old repl. I suppose OP used new repl, enabled in the CPython 3.13 by default, see: https://docs.python.org/3.13/whatsnew/3.13.html#a-better-interactive-interpreter

[ImFeH2]

I hope this message finds you well. I was wondering if anyone is currently addressing this issue. If it’s alright, would it be possible for me to create a PR? I may already find the cause of the mistake.
Thank you!

[skirpichev]

@ImFeH2, sure. So far nobody confirm that can reproduce issue.

Feel free to open a PR, see also https://devguide.python.org/getting-started/pull-request-lifecycle/#making-good-prs