After exiting ipy, readline tab-completion is broken when using gnureadline + Python 3.13

[tleonhardt]

After exiting ipy ipython shell, prompt color and tab completion are messed up.

Tested on 3.0.0 branch with an example application and verified behavior is the same on the master branch.

Tested on macOS Sequoia 15.1 using Python 3.13.0. Used multiple different terminals and behavior was the same.

The problem does not happen when using Python 3.12.7 on the exact same setup.

The problem does happen on Linux when using gnureadline + Python 3.13.

Hence the bug is specific to the combination of gnureadline + Python 3.13 + ipython

[tleonhardt]

After much debugging by commenting out code, the code that breaks everything is:

from IPython import (  # type: ignore[import]
    start_ipython,
)

[tleonhardt]

I verified this bug is also impacting the master branch

[tleonhardt]

This problem is not happening when using Python 3.12.7 with the exact same setup on macOS Sequoia 15.1 and testing on the master branch.

I also verified it is still happening when using Python 3.13.0 on the same system in a freshly created virtual environment.

I installed everything using pipenv and this includes the gnureadline package. Without that package, macOS has libedit and tab completion doesn't work at all and cmd2 emits a warning message about readline features being disabled. I also used pip freeze to verify gnureadline==8.2.13 is the version installed which is the latest.

[tleonhardt]

I tested in a fresh Python 3.13 venv installed using pipenv on a minimal python Docker container and this problem does not exist.

Hence from existing testing, it is limited to the following combination:

• macOS
• Python 3.13
• gnureadline

It would be interesting to temporarily tweak our code to prefer using python-gnureadline on Linux and test there. I'm not sure if the bug is specific to macOS + Python 3.13 or gnureadline + Python 3.13

[tleonhardt]

I just verified in a minimal python Docker container that this bug happens on Linux when using Python 3.13 and gnureadline.

Hence this bug is very specific to the combination of gnureadline + Python 3.13

[tleonhardt]

I used a cmd2 app with both py and ipy commands to inspect sys.modules after exiting ipy using py and found readline still points to gnureadline:

sys.modules['readline']
<module 'gnureadline' from '/Users/toddleonhardt/src/python/cmd2/.venv/lib/python3.13/site-packages/[gnureadline.cpython-313-darwin.so](http://gnureadline.cpython-313-darwin.so/)'>

[anselor]

Is this something gnureadline needs to fix?

[tleonhardt]

I'm not sure yet if the problem is fundamentally in gnureadline, ipython, or readline itself. But I'm continuing to investigate with help from @kmvanbrunt .

We are also looking to see if there is a way we can recover from it.

[tleonhardt]

When it happens there are two side-effects visible to the user:

1. All tab-completion is broken and hitting tab just inserts a tab
2. Any color in the prompt is gone

[tleonhardt]

Executing readline.parse_and_bind(self.completekey + ": complete") right before returning from ipy didn't help.

Doing from IPython import start_ipython at the top of cmd2.py before importing anything from our custom cmd2 code does fix the problem. The only problem there is we have also said ipython is an optional dependency and this would make it a required one. I guess we should wrap that in a try.

[tleonhardt]

8.2.13 is the first version of gnureadline to support Python 3.13, so I can't install an older version using Python 3.13

I did verify that version 8.2.13 of gnureadline doesn't have this problem when running with Python 3.12.7.