bug#68559: [PATCH] Improve Python shell completion

[Liu Hui]

On Fri, Feb 16, 2024 at 12:37 AM Eli Zaretskii <eliz@gnu.org> wrote:
>
> > From: Mattias Engdegård <mattias.engdegard@gmail.com>
> > Date: Thu, 15 Feb 2024 15:43:32 +0100
> > Cc: Eli Zaretskii <eliz@gnu.org>,
> >  kobarity@gmail.com,
> >  68559@debbugs.gnu.org
> > The recent change on master, 0b9c7148fd, causes several failures in 
> > python-tests here (macOS). Log attached.
> >
> > It seems to have something to do with completion. Maybe the new code is 
> > sensitive to details of Python's command line editor? The standard Python 
> > interpreter is unlikely to use GNU readline, for example.
>
> The python-*-completion-at-point-* tests never worked for me, and I
> always assumed it was something specific to MS-Windows.  But maybe
> not.  There was no change in the tests that fail for me before and
> after the recent changes related to Python.

The Python shell completion relies on the readline module, which is
not available for Python on MS-Windows. According to the instruction
in python.el:

;; readline based shell (it's known to work with PyPy).  If your
;; Python installation lacks readline (like CPython for Windows),
;; installing pyreadline (URL `https://ipython.org/pyreadline.html')
;; should suffice.  To troubleshoot why you are not getting any
;; completions, you can try the following in your Python shell:

;; >>> import readline, rlcompleter

;; If you see an error, then you need to either install pyreadline or
;; setup custom code that avoids that dependency.

It may be necessary to install pyreadline (for Python 2.7) or
pyreadline3 (for Python 3).