GNU bug report logs - #43450
28.0.50; Python shell doesn't echo if shebang

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Gunnar Horrigmo <horrigmo <at> runbox.no>
To: bug-gnu-emacs <at> gnu.org
Subject: 28.0.50; Python shell doesn't echo if shebang
Date: Wed, 16 Sep 2020 15:23:22 +0200

Open a .py file
M-x run-python RET
In .py file, write some statement, say "1+2" and evaluate it with
(f.ex.) python-shell-send-statement. Observe that python shell echoes
the result, "3", and prompts on a new line.

Add a shebang to the top of .py file (f.ex. "#!/usr/bin/pyton3" on my
system). Evaluate the same statement as over. Observe that python shell
doesn't echo the result, but does print a new prompt, but without a
newline. 

You can add and remove the shebang as much you want, and see the echo
behaviour change accordingly. You do _not_ need to save the file.

You can see a replay of the issue here:
https://asciinema.org/a/DOq15ldlyiKI5HKLrKpF7gIeg

I've verified this behaviour using emacs -Q on versions 28.0.50
(including master HEAD as of 2020-09-16) and 27.1.50. And it seems all
the python-shell-send-* functions exhibit the same, not just
python-shell-send-statement. 



In GNU Emacs 28.0.50 (build 4, x86_64-pc-linux-gnu, GTK+ Version 3.24.13, cairo version 1.16.0)
 of 2020-05-23 built on hot-rats.uio.no
Repository revision: f8581bcf6a1942ebd331cae20e32945a3a86a3d1
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Fedora 31 (Workstation Edition)

Recent messages:
Checking 71 files in /home/horrigmo/src/emacs/emacs/lisp/erc...
Checking 34 files in /home/horrigmo/src/emacs/emacs/lisp/emulation...
Checking 180 files in /home/horrigmo/src/emacs/emacs/lisp/emacs-lisp...
Checking 24 files in /home/horrigmo/src/emacs/emacs/lisp/cedet...
Checking 59 files in /home/horrigmo/src/emacs/emacs/lisp/calendar...
Checking 87 files in /home/horrigmo/src/emacs/emacs/lisp/calc...
Checking 105 files in /home/horrigmo/src/emacs/emacs/lisp/obsolete...
Checking for load-path shadows...done
C-x C-g is undefined [2 times]
Buffer *unsent mail to bug-gnu-emacs <at> gnu.org* modified; kill anyway? (y or n) y

Configured features:
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ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS PDUMPER LCMS2
GMP

Important settings:
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Major mode: ERC

Minor modes in effect:
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Load-path shadows:
None found.

Features:
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Memory information:
((conses 16 441208 78375)
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-- 
Gunnar

Message #8 received at 43450 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Gunnar Horrigmo <horrigmo <at> runbox.no>
Cc: Fabián Ezequiel Gallina <fgallina <at> gnu.org>,
 43450 <at> debbugs.gnu.org
Subject: Re: bug#43450: 28.0.50; Python shell doesn't echo if shebang
Date: Wed, 30 Sep 2020 18:50:16 +0200

Gunnar Horrigmo <horrigmo <at> runbox.no> writes:

> Open a .py file
> M-x run-python RET
> In .py file, write some statement, say "1+2" and evaluate it with
> (f.ex.) python-shell-send-statement. Observe that python shell echoes
> the result, "3", and prompts on a new line.
>
> Add a shebang to the top of .py file (f.ex. "#!/usr/bin/pyton3" on my
> system). Evaluate the same statement as over. Observe that python shell
> doesn't echo the result, but does print a new prompt, but without a
> newline. 

I can reproduce this in Emacs 28, but it doesn't seem to be triggered by
the shebang:  Adding some blank lines to the top of the buffer also
triggers the error.  Or ... anything:

(python-shell-buffer-substring 2 (point) nil)
=> "# -*- coding: utf-8 -*-

1+2"

(python-shell-buffer-substring 1 (point) nil)
=> "1+2"

         (fillstr (when (not starts-at-point-min-p)
                    (concat
                     (format "# -*- coding: %s -*-\n" encoding)
                     (make-string
                      ;; Subtract 2 because of the coding cookie.
                      (- (line-number-at-pos start) 2) ?\n)))))

This was added by (in a slightly different form):

commit 2dd5163d764f395eb31a2306dba385d123af4aba
Author:     Fabián Ezequiel Gallina <fgallina <at> gnu.org>
AuthorDate: Sat Dec 27 01:30:21 2014 -0300

    python.el: Handle file encoding for shell.
    
    * lisp/progmodes/python.el (python-rx-constituents): Add coding-cookie.
    (python-shell--save-temp-file): Write file with proper encoding.
    (python-shell-buffer-substring): Add coding cookie for detected
    encoding to generated content.  Fix blank lines when removing
    if-name-main block.
    (python-shell-send-file): Handle file encoding.
    (python-info-encoding-from-cookie)
    (python-info-encoding): New functions.

I've added Fabián to the Cc, perhaps he has some insight here...

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #11 received at 43450 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Gunnar Horrigmo <horrigmo <at> runbox.no>
Cc: Fabián Ezequiel Gallina <fgallina <at> gnu.org>,
 43450 <at> debbugs.gnu.org
Subject: Re: bug#43450: 28.0.50; Python shell doesn't echo if shebang
Date: Fri, 02 Oct 2020 05:33:04 +0200

Lars Ingebrigtsen <larsi <at> gnus.org> writes:

> I can reproduce this in Emacs 28, but it doesn't seem to be triggered by
> the shebang:  Adding some blank lines to the top of the buffer also
> triggers the error.  Or ... anything:
>
> (python-shell-buffer-substring 2 (point) nil)
> => "# -*- coding: utf-8 -*-
>
> 1+2"

I have to admit that I don't understand the reason for the coding cookie
at all -- we bind coding-system-for-write to utf-8 before writing the
temp file anyway, and on the Python side, we specify the coding system
explicitly there, too.

But in case it does have an effect, I haven't removed it altogether, but
instead made the C-c C-e command avoid outputting it, which fixes the
problem.  C-M-x, probably a more important command, is not affected by
the cookie one way or another (since it's just side-effecting), so I've
left it alone there.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #18 received at 43450 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Gunnar Horrigmo <horrigmo <at> runbox.no>
Cc: 43450 <at> debbugs.gnu.org
Subject: Re: bug#43450: 28.0.50; Python shell doesn't echo if shebang
Date: Fri, 02 Oct 2020 05:40:37 +0200

Lars Ingebrigtsen <larsi <at> gnus.org> writes:

> I have to admit that I don't understand the reason for the coding cookie
> at all -- we bind coding-system-for-write to utf-8 before writing the
> temp file anyway, and on the Python side, we specify the coding system
> explicitly there, too.

OK, I think this is basically the point of it all:

(defun python-shell--save-temp-file (string)
  (let* ((temporary-file-directory
          (if (file-remote-p default-directory)
              (concat (file-remote-p default-directory) "/tmp")
            temporary-file-directory))
         (temp-file-name (make-temp-file "py"))
         (coding-system-for-write (python-info-encoding)))
    (with-temp-file temp-file-name
      (insert string)
      (delete-trailing-whitespace))
    temp-file-name))

If the current buffer has a coding cookie, we use that in the temp files
we load, too.  That's logical (er, somewhat, why not just use the
current buffer coding system?), but if there's no coding cookie, we
still add one, which isn't.

Anyway, I think the change I made is unlikely to break anything...
possibly...  unless you have a Python file with a coding system cookie,
and you're eval-ing a non-ASCII string, and it's not all utf-8.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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