GNU bug report logs - #72750
29.3; indent-region changes semantics of python code

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

From: Michael Arndt <michael <at> rndt.dev>
To: bug-gnu-emacs <at> gnu.org
Subject: 29.3; indent-region changes semantics of python code
Date: Wed, 21 Aug 2024 20:06:52 +0200

Hi,

I have a problem when indenting python files. There seems to be a case
when using indent-region changes the semantics of the python code. When
there is no blank line after an if-statement, the next line becomes part
of the if statement.

The problem can be reproduced by the following steps:

1. Start emacs -Q
2. Create a python file with the following contents:

if False:
     print("output1")
print("output2")

3. Use M-x mark-whole-buffer
4. Use M-x indent-region
5. The file contents change into:

if False:
     print("output1")
     print("output2")

The problem can be avoided by adding a blank line after the if statement.
Because I use a custom indentation function that calls (indent-region
(point-min) (point-max)) this can happen pretty quickly. Is this a
limitation of python-indent-region?

Greetings
Michael


In GNU Emacs 29.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 2.24.33,
cairo version 1.18.0) of 2024-04-02 built on titan
Repository revision: ae8f815613c2e072e92aa8fe7b4bcf2fdabc7408
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Windowing system distributor 'The X.Org Foundation', version 11.0.12101011
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Message #8 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Andreas Röhler <andreas.roehler <at> easy-emacs.de>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: bug#72750: 29.3; indent-region changes semantics of python code
Date: Fri, 23 Aug 2024 20:52:42 +0200

[Message part 1 (text/plain, inline)]

Am 21.08.24 um 20:06 schrieb Michael Arndt via Bug reports for GNU 
Emacs, the Swiss army knife of text editors:
> Hi,
>
> I have a problem when indenting python files. There seems to be a case
> when using indent-region changes the semantics of the python code. When
> there is no blank line after an if-statement, the next line becomes part
> of the if statement.
>
> The problem can be reproduced by the following steps:
>
> 1. Start emacs -Q
> 2. Create a python file with the following contents:
>
> if False:
>      print("output1")
> print("output2")
>
> 3. Use M-x mark-whole-buffer
> 4. Use M-x indent-region
> 5. The file contents change into:
>
> if False:
>      print("output1")
>      print("output2")
>
> The problem can be avoided by adding a blank line after the if statement.
> Because I use a custom indentation function that calls (indent-region
> (point-min) (point-max)) this can happen pretty quickly. Is this a
> limitation of python-indent-region?
>
> Greetings
> Michael
>
>
Hi Michael,

I'm not maintaining the related code, just a comment:

as indent might by syntax at Python, there is not way for 
auto-formatting - unless you are happy with the outmost reasonable indent.

|Best,|

|Andreas
|

[Message part 2 (text/html, inline)]

Message #11 received at 72750 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Michael Arndt <michael <at> rndt.dev>, 72750 <at> debbugs.gnu.org
Cc: kobarity <kobarity <at> gmail.com>
Subject: Re: bug#72750: 29.3; indent-region changes semantics of python code
Date: Sat, 21 Sep 2024 07:56:47 -0400

Michael Arndt via "Bug reports for GNU Emacs, the Swiss army knife of
text editors" <bug-gnu-emacs <at> gnu.org> writes:

> I have a problem when indenting python files. There seems to be a case
> when using indent-region changes the semantics of the python code. When
> there is no blank line after an if-statement, the next line becomes part
> of the if statement.
>
> The problem can be reproduced by the following steps:
>
> 1. Start emacs -Q
> 2. Create a python file with the following contents:
>
> if False:
>       print("output1")
> print("output2")
>
> 3. Use M-x mark-whole-buffer
> 4. Use M-x indent-region
> 5. The file contents change into:
>
> if False:
>       print("output1")
>       print("output2")
>
> The problem can be avoided by adding a blank line after the if statement.
> Because I use a custom indentation function that calls (indent-region
> (point-min) (point-max)) this can happen pretty quickly. Is this a
> limitation of python-indent-region?

I'm not sure that I see a bug here.  I don't think one can generally
expect `indent-region` to be able to avoid changing semantics in a
language where indentation matters.

I'm copying in kobarity, in case he has any comments.

Message #14 received at 72750 <at> debbugs.gnu.org (full text, mbox):

From: kobarity <kobarity <at> gmail.com>
To: Stefan Kangas <stefankangas <at> gmail.com>, Michael Arndt <michael <at> rndt.dev>
Cc: 72750 <at> debbugs.gnu.org
Subject: Re: bug#72750: 29.3; indent-region changes semantics of python code
Date: Sat, 21 Sep 2024 23:51:00 +0900

Stefan Kangas wrote:
> Michael Arndt via "Bug reports for GNU Emacs, the Swiss army knife of
> text editors" <bug-gnu-emacs <at> gnu.org> writes:
> 
> > I have a problem when indenting python files. There seems to be a case
> > when using indent-region changes the semantics of the python code. When
> > there is no blank line after an if-statement, the next line becomes part
> > of the if statement.
> >
> > The problem can be reproduced by the following steps:
> >
> > 1. Start emacs -Q
> > 2. Create a python file with the following contents:
> >
> > if False:
> >       print("output1")
> > print("output2")
> >
> > 3. Use M-x mark-whole-buffer
> > 4. Use M-x indent-region
> > 5. The file contents change into:
> >
> > if False:
> >       print("output1")
> >       print("output2")
> >
> > The problem can be avoided by adding a blank line after the if statement.
> > Because I use a custom indentation function that calls (indent-region
> > (point-min) (point-max)) this can happen pretty quickly. Is this a
> > limitation of python-indent-region?
> 
> I'm not sure that I see a bug here.  I don't think one can generally
> expect `indent-region` to be able to avoid changing semantics in a
> language where indentation matters.

I agree.  Even though `python-indent-region' can be improved to some
extent, it seems to me that it is better to use an external tool like
"black" to preserve the semantics and format the entire buffer.

Message #17 received at 72750 <at> debbugs.gnu.org (full text, mbox):

From: Michael Arndt <michael <at> rndt.dev>
To: kobarity <kobarity <at> gmail.com>, Stefan Kangas <stefankangas <at> gmail.com>
Cc: 72750 <at> debbugs.gnu.org
Subject: Re: bug#72750: 29.3; indent-region changes semantics of python code
Date: Sat, 21 Sep 2024 18:03:42 +0200

[Message part 1 (text/plain, inline)]

On 21.09.24 16:51, kobarity wrote:
> I agree.  Even though `python-indent-region' can be improved to some
> extent, it seems to me that it is better to use an external tool like
> "black" to preserve the semantics and format the entire buffer.
That's fine for me too. I will use something like `eglot-format' to 
format my python files instead. Thank you.

[Message part 2 (text/html, inline)]

Message #20 received at 72750 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefankangas <at> gmail.com>
To: Michael Arndt <michael <at> rndt.dev>, kobarity <kobarity <at> gmail.com>
Cc: 72750 <at> debbugs.gnu.org
Subject: Re: bug#72750: 29.3; indent-region changes semantics of python code
Date: Sat, 21 Sep 2024 18:05:52 -0700

tags 72750 + notabug wontfix
close 72750
thanks

Michael Arndt <michael <at> rndt.dev> writes:

> On 21.09.24 16:51, kobarity wrote:
>> I agree.  Even though `python-indent-region' can be improved to some
>> extent, it seems to me that it is better to use an external tool like
>> "black" to preserve the semantics and format the entire buffer.
> That's fine for me too. I will use something like `eglot-format' to
> format my python files instead. Thank you.

You could also try the package `blacken`:

    https://github.com/pythonic-emacs/blacken

I'm closing this bug report.

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