bug#32120: 26.1; In python.el tab-width should default to 4

bug#32120: 26.1; In python.el tab-width should default to 4

[Carlos Pita]

Most python source code uses a tab step of 4 spaces. I think it doesn't
make a lot of sense to default tab-width to 4. Maybe there is a reason
I'm failing to grasp.

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bug#32120: 26.1; In python.el tab-width should default to 4

[Robert Pluim]

Carlos Pita <carlosjosepita@gmail.com> writes:

> Most python source code uses a tab step of 4 spaces.

This:

>I think it doesn't
> make a lot of sense to default tab-width to 4.

is in contrast with the bug title, which is

    tab-width should default to 4

python.el defaults tab-width to 8, but sets indent-tabs-mode to nil,
and uses an indent of 4 for me from emacs -Q (by using
python-indent-offset autodetection).

What would you like changed?

Regards

Robert

bug#32120: 26.1; In python.el tab-width should default to 4

[Carlos Pita]

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>
>
> >I think it doesn't
> > make a lot of sense to default tab-width to 4.
>

Sorry, s/4/8/ here.

>
>
> python.el defaults tab-width to 8, but sets indent-tabs-mode to nil,
>

When you do rigid indentation, say C-x Tab and then S-Right, you get
8-spaces tab steps with that configuration.

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bug#32120: 26.1; In python.el tab-width should default to 4

[Glenn Morris]

Carlos Pita wrote:

> When you do rigid indentation, say C-x Tab and then S-Right, you get
> 8-spaces tab steps with that configuration.

Right. What is your justification for wanting this to be 4?
Python generally discourages tabs, but when they are present, seems to
follow the historical convention mapping them to 8 spaces. Eg

https://docs.python.org/3/reference/lexical_analysis.html#indentation

    Tabs are replaced (from left to right) by one to eight spaces such
    that the total number of characters up to and including the
    replacement is a multiple of eight (this is intended to be the same
    rule as used by Unix).

bug#32120: 26.1; In python.el tab-width should default to 4

[Carlos Pita]

> Right. What is your justification for wanting this to be 4?
> Python generally discourages tabs, but when they are present, seems to
> follow the historical convention mapping them to 8 spaces.

Sure, I don't want to enter tab characters at all, I just want to
rigidly indent using 4-space tab stops. And setting tab-width to 4 and
indent-tabs-mode to nil makes C-x Tab S-Right do just that.

bug#32120: 26.1; In python.el tab-width should default to 4

[Glenn Morris]

I guess this is why python-indent-shift-left/right exist.
They indent by python-indent-offset (ie 4), not tab-width.
ISTM that tab-width should remain 8.

bug#32120: 26.1; In python.el tab-width should default to 4

[Carlos Pita]

Ok, I didn't know about those python specific functions!

Nevertheless I fail to see why you prefer a tab width of 8, but my
immediate problem is solved.

Thanks!

bug#32120:

[Carlos Pita]

Some months later, I'm insisting on this.

I don't see any point in setting the default to 8 when:

1. PEP 8 clearly states: use 4 spaces per indentation level.
2. Python mode specific rigid indentation mechanism defaults to 4 spaces.

AFAICS the only thing you get by setting tab-width to 8 is
incompatibility of emacs standard rigid indentation mechanism (M-x
Tab) with both 1 and 2. I think it's important to play well with
standard facilities (despite python mode providing it's own variant)
and, in any case, there is no good reason, no trade off, not to do it.

bug#32120: 26.1; In python.el tab-width should default to 4

[Noam Postavsky]

Carlos Pita <carlosjosepita@gmail.com> writes:

>> Right. What is your justification for wanting this to be 4?
>> Python generally discourages tabs, but when they are present, seems to
>> follow the historical convention mapping them to 8 spaces.

>> https://docs.python.org/3/reference/lexical_analysis.html#indentation
>>
>>     Tabs are replaced (from left to right) by one to eight spaces such
>>     that the total number of characters up to and including the
>>     replacement is a multiple of eight (this is intended to be the same
>>     rule as used by Unix).

> Sure, I don't want to enter tab characters at all, I just want to
> rigidly indent using 4-space tab stops. And setting tab-width to 4 and
> indent-tabs-mode to nil makes C-x Tab S-Right do just that.

> Some months later, I'm insisting on this.
>
> I don't see any point in setting the default to 8 when:
>
> 1. PEP 8 clearly states: use 4 spaces per indentation level.
> 2. Python mode specific rigid indentation mechanism defaults to 4 spaces.
>
> AFAICS the only thing you get by setting tab-width to 8 is
> incompatibility of emacs standard rigid indentation mechanism (M-x
> Tab) with both 1 and 2. I think it's important to play well with
> standard facilities (despite python mode providing it's own variant)
> and, in any case, there is no good reason, no trade off, not to do it.

Seems clear to me that the proper solution is simply to rebind C-x Tab
S-left/right to use python-indent-shift-left/right.  That will solve the
actual problem you experience, without incorrectly showing any existing
tab charaters as 4 spaces.

bug#32120: 26.1; In python.el tab-width should default to 4

[Carlos Pita]

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Hi Noam,

On Sat, Mar 30, 2019 at 12:17 AM Noam Postavsky <npostavs@gmail.com> wrote:

>
> Seems clear to me that the proper solution is simply to rebind C-x Tab
> S-left/right to use python-indent-shift-left/right.  That will solve the
> actual problem you experience, without incorrectly showing any existing
> tab charaters as 4 spaces.
>
>
 I would agree with you if I understood why is it incorrect to show 4
spaces for a tab. OTOH I'm not saying it is correct, just that it would be
more consistent with a (suggested by a PEP) 4-space indentation step.

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bug#32120: 26.1; In python.el tab-width should default to 4

[Noam Postavsky]

Carlos Pita <carlosjosepita@gmail.com> writes:

> On Sat, Mar 30, 2019 at 12:17 AM Noam Postavsky <npostavs@gmail.com> wrote:
>
>>
>> Seems clear to me that the proper solution is simply to rebind C-x Tab
>> S-left/right to use python-indent-shift-left/right.  That will solve the
>> actual problem you experience, without incorrectly showing any existing
>> tab charaters as 4 spaces.
>>
>>
>  I would agree with you if I understood why is it incorrect to show 4
> spaces for a tab.

Because, as Glenn mentioned, the Python spec specifically says that tabs
should be 8 spaces.

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=32120#14

bug#32120: 26.1; In python.el tab-width should default to 4

[Carlos Pita]

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Ah ok, it seems to me that when he mentioned that I was somehow confused
about the role of tab-width regarding tab steps and, later, I'd probably
forgotten about that part of the reference and was thinking about the PEP
only. I'm closing this then. Thanks!

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bug#32120: 26.1; In python.el tab-width should default to 4

[Carlos Pita]

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> And setting tab-width to 4 and indent-tabs-mode to nil makes C-x Tab
S-Right do just that.

My suggestion at the time included disabling indent-tabs, so it was ok.
Then I forgot about that. Anyway, considering that again, I'm not as
convinced about my earlier proposal.

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bug#32120: 26.1; In python.el tab-width should default to 4

[Stefan Kangas]

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tags 32120 + notabug
close 32120
quit

Carlos Pita <carlosjosepita@gmail.com> writes:

> Ah ok, it seems to me that when he mentioned that I was somehow
> confused about the role of tab-width regarding tab steps and, later,
> I'd probably forgotten about that part of the reference and was
> thinking about the PEP only. I'm closing this then. Thanks!

The conclusion of the discussion was that this should be closed, but it
was never done at the time.  I'm therefore closing this now.

Best regards,
Stefan Kangas

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