bug#45655: Please use 'python3' command instead of 'python'

[Glenn Morris]

Balint Reczey wrote:

> Python 2 reached EOL about a year ago thus the 'python' command may be
> missing on some systems. 'python3' is the standard way of invoking the
> Python 3 interpreter, thus Emacs would have a better chance trying
> that.
>
> The attached patch is already carried in Ubuntu.

Thanks for the report.

> --- a/lisp/ldefs-boot.el
> +++ b/lisp/ldefs-boot.el
> @@ -26539,7 +26539,7 @@
>  
>  (add-to-list 'interpreter-mode-alist (cons (purecopy "python[0-9.]*") 
> 'python-mode))
>  
> -(autoload 'run-python "python" "\
> +(autoload 'run-python "python3" "\

This bit is wrong. Firstly, ldefs-boot is a generated file, and
secondly, unless Ubuntu is distributing a python3.el, it would just
break the autoload.

> --- a/lisp/progmodes/python.el
> +++ b/lisp/progmodes/python.el
> @@ -1952,7 +1952,7 @@
>    :group 'python
>    :safe 'stringp)
>  
> -(defcustom python-shell-interpreter "python"
> +(defcustom python-shell-interpreter "python3"

(if (executable-find "python3") "python3" "python")

is probably how Emacs would normally handle this kind of thing.
Or if defaulting to python3 is better (I guess it is):

(cond ((executable-find "python3") "python3")
      ((executable-find "python") "python")
      (t "python3"))