PEP 7 (or guide) add C style policies and explanation

[terryjreedy]

BPO	12188
Nosy	@gvanrossum, @terryjreedy, @pitrou, @vstinner, @ericvsmith, @ezio-melotti, @tonybaloney

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-05-09.01:07:47.627>
created_at = <Date 2011-05-26.18:19:32.365>
labels = ['docs']
title = 'PEP 7 (or guide) add C style policies and explanation'
updated_at = <Date 2019-05-09.01:07:47.620>
user = 'https://github.com/terryjreedy'

bugs.python.org fields:

activity = <Date 2019-05-09.01:07:47.620>
actor = 'anthonypjshaw'
assignee = 'docs@python'
closed = True
closed_date = <Date 2019-05-09.01:07:47.627>
closer = 'anthonypjshaw'
components = ['Documentation']
creation = <Date 2011-05-26.18:19:32.365>
creator = 'terry.reedy'
dependencies = []
files = []
hgrepos = []
issue_num = 12188
keywords = []
message_count = 8.0
messages = ['136991', '137111', '137808', '137809', '137814', '137818', '138143', '341951']
nosy_count = 8.0
nosy_names = ['gvanrossum', 'terry.reedy', 'pitrou', 'vstinner', 'eric.smith', 'ezio.melotti', 'docs@python', 'anthonypjshaw']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue12188'
versions = ['Python 2.7', 'Python 3.2', 'Python 3.3']

[terryjreedy]

In response to a discussion of a patch removing 'useless' post-increments, (which issue has apparently come up before)
Guido posted
"> Sorry to butt in here, but I agree with Eric that it was better

before. There is a common idiom, *pointer++ =<something>, and
whenever you see that you know that you are appending something to an
output buffer. Perhaps the most important idea here is that this
maintains the *invariant* "pointer points just after the last thing in
the buffer". Always maintaining the invariant is better than trying to
micro-optimize things so as to avoid updating dead values. The
compiler is better at that."

A condensed version of the above added to PEP-7 would help new developers see the usage as local idiom rather than style bug.

[ezio-melotti]

I'm not sure it's worth adding this to the PEP-7. The PEP is about conventions and style not idioms.
PEP-8 has a section about "Programming Recommendations" that contains a few idioms, but since PEP-7 doesn't have an equivalent section, I think that explaining this idiom (and not others) will look out of place.

[pitrou]

Indeed, I don't think that's appropriate. Also, it's not about ++ in general but a particular use of it.

[ericvsmith]

But don't you think we should put information like this somewhere, even if it's not in PEP-7? We've had a discussion about this particular issue (idiomatic pointer increments when appending to a buffer) at least twice, and there's also the recent "if (const == variable)" issue that feels similar to me.

It seems to me that recording these decisions somewhere has value, just so we don't have to revisit them.

[ezio-melotti]

If there are a few of these idioms, I'm not against adding a new section to PEP-7 (something like the "Programming Recommendations" section in the PEP-8). It's just not worth doing it for the "*p++ = x;" idiom alone IMHO.

[pitrou]

If there are a few of these idioms, I'm not against adding a new
section to PEP-7 (something like the "Programming Recommendations"
section in the PEP-8). It's just not worth doing it for the "*p++ =
x;" idiom alone IMHO.

If these are recommandations, perhaps we should put them in the devguide
instead?

But I agree that it's not worth doing it only for "*p++" anyway.

[terryjreedy]

We have a second item for the PEP (or Guide) section (but I think I prefer in the PEP so as to have one place to look for such things.).
So I changed the title a bit.

On 6/10/2011 3:49 PM, Guido van Rossum wrote:

On Wed, Jun 8, 2011 at 8:12 AM, Nick Coghlan<ncoghlan@gmail.com>
> I actually thought Brett's rationale in the checkin comment was
> reasonable (if you get in the habit of putting constants on the left,
> then the classic "'=' instead of '=='" typo is a compiler error
> instead of a reassignment).

[I understand this rationale too; I forget what I actually did when I was writing C.]

I really like consistency across the code base. I really don't like
constant-on-the-left, and it's basically not used in the current
codebase. Please be consistent and don't start using it.

[I suspect I did this.]

> Call it a +0 in favour of letting people put constants on the left in
> C code if they prefer it that way, so long as any given if/elif chain
> is consistent in the style it uses.

Sorry, I give it a -1. (I'd like to be able to read the codebase still... :-)

I bet there will be more things for a new section.

[tonybaloney]

Hi,

This discussion came to a stop, but it doesn't seem conclusive.

PEP discussions are now in GitHub on https://github.com/python/peps/issues so I'm going to close this BPO issue.

There is no additional section in PEP-7 for this level of detail, there is also no tooling in place (afaik) to retroactively apply or inspect these types of issues, so this would need to be discussed in the PEP issue,