Add `readline.backend` for the backend `readline` uses

[gaogaotiantian]

Feature or enhancement

Proposal:

Currently we support two backends with readline: GNU readline and editline. They work in a similar way but have some differences. Notably the way to set <tab> as the complete key.

The users need to distinguish the backend at run time, and currently the recommended way is:

if 'libedit' in getattr(readline, '__doc__', ''):

We have worse checks like

readline_doc = getattr(readline, '__doc__', '')
if readline_doc is not None and 'libedit' in readline_doc:

in site.py.

It would be nice to provide a more official and clean way to check the backend, instead of querying for the docstring for the module. This is also mentioned in #107748 (comment) by @encukou .

In this proposal, a new attribute backend is added which could be either readline or editline.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-112510: Add readline.backend for the backend readline uses #112511

[encukou]

Thank you for adding it!

[whitequark]

Could readline.backend be backported to 3.12? It seems that several popular builds of Python (from what I can tell, at least Homebrew and python-build-standalone) have switched to libedit and projects using the builtin readline module functionality are now hitting #121160. It would help if the __doc__ workaround was made unnecessary earlier.

[gaogaotiantian]

I believe Mac is using libedit by default. Unfortunately, this is considered a new feature and I don't think it would be backported to 3.12.

[whitequark]

Thanks, this is good to know at least.