Update PEP-8 regarding binary operators

[IanLee1521]

BPO	26763
Nosy	@gvanrossum, @warsaw, @methane, @Rosuav, @berkerpeksag, @IanLee1521
Files	wrap-before-binary-operator.patch: Update PEP-8 to specify wrapping before rather than after a binary operator

^{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 2016-04-15.16:46:46.580>
created_at = <Date 2016-04-15.07:06:00.535>
labels = ['type-feature']
title = 'Update PEP-8 regarding binary operators'
updated_at = <Date 2016-04-15.19:24:01.590>
user = 'https://github.com/IanLee1521'

bugs.python.org fields:

activity = <Date 2016-04-15.19:24:01.590>
actor = 'Rosuav'
assignee = 'none'
closed = True
closed_date = <Date 2016-04-15.16:46:46.580>
closer = 'gvanrossum'
components = []
creation = <Date 2016-04-15.07:06:00.535>
creator = 'IanLee1521'
dependencies = []
files = ['42463']
hgrepos = []
issue_num = 26763
keywords = ['patch']
message_count = 17.0
messages = ['263453', '263454', '263455', '263489', '263490', '263495', '263497', '263498', '263499', '263501', '263506', '263508', '263509', '263510', '263518', '263519', '263520']
nosy_count = 7.0
nosy_names = ['gvanrossum', 'barry', 'methane', 'Rosuav', 'berker.peksag', 'IanLee1521', 'Mart\xc3\xadn Gait\xc3\xa1n']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'patch review'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue26763'
versions = []

[IanLee1521]

Following up from discussion on python-ideas [1] about updating PEP-8 regarding wrapping lines before rather than after binary operators.

[IanLee1521]

Discussion link missing from msg263453: https://mail.python.org/pipermail/python-ideas/2016-April/039774.html

[IanLee1521]

Link to GitHub branch with the patch as a commit [1].

[1] python/peps@master...IanLee1521:bpo-26763

[methane]

python/peps@master...IanLee1521:bpo-26763

[methane]

Roundup doesn't link to Github's branch comparing URL correctly.
How about just create pull request on Github?

[berkerpeksag]

Please don't create a pull request on GitHub (python/peps is read-only). Attaching wrap-before-binary-operator.patch is enough.

[methane]

How about recommend using parentheses to avoid different level operators have same indent level?

ok:
if (width == 0
and height == 0
and color == 'red'
and emphasis == 'strong'
or highlight > 100
):
...

better:
if ((width == 0
and height == 0
and color == 'red'
and emphasis == 'strong')
or highlight > 100
):

[gvanrossum]

I don't like the way "):" is indented in that example. I propose:

        if ((width == 0
             and height == 0
             and color == 'red'
             and emphasis == 'strong')
            or highlight > 100):

Aren't there many other examples in the PEP that need to be adjusted, since we're changing the style not just for 'and' and 'or' but for all binary operators?

[gvanrossum]

I also think the PEP needs some language about the previous style being still acceptable as long as it's being used consistently (Knuth notwithstanding), and an acceptable compromise style where and/or go at the start of the line but other binary operators stay at the end.

[methane]

On Fri, Apr 15, 2016 at 11:31 PM, Guido van Rossum <report@bugs.python.org>
wrote:

Guido van Rossum added the comment:

I don't like the way "):" is indented in that example.

Me too.
I haven't know about this PEP-8 update.
python/peps@843b7d2

I propose:

        if ((width == 0
             and height == 0
             and color == 'red'
             and emphasis == 'strong')
            or highlight \> 100):

Looks better to me. But how about this?

if (width == 0
and height == 0
and color == 'red'
and emphasis == 'strong'
or highlight > 100):

Changing indentation level based on operator precedence is acceptable?

[gvanrossum]

Changing indentation level based on operator precedence is acceptable?

I think that's a matter of personal taste and I don't think the PEP needs to have an opinion on it.

[gvanrossum]

I've updated the PEP with some more permissive language, mentioning Knuth's recommendation but allowing the old style because it's been recommended (and followed, and enforced) for decades. I've intentionally not updated other examples in the PEP to follow suit.

[IanLee1521]

Aren't there many other examples in the PEP that need to be adjusted, since we're changing the style not just for 'and' and 'or' but for all binary operators?

Admittedly I'd only looked in that one section last night, but I just went through the PEP and didn't see any other when I just went through the entire PEP now...

I also think the PEP needs some language about the previous style being still acceptable as long as it's being used consistently (Knuth notwithstanding), and an acceptable compromise style where and/or go at the start of the line but other binary operators stay at the end.

I'd updated my branch on GitHub [1] but Guido, you beat me to the update while I was typing this message!

I don't like the way "):" is indented in that example.

Honestly I don't either, I just like it more than artificially pushing the other lines forward a space. Personally, I'm not a fan of the current change either which puts the raise in line with the condition logic for the if::

    if (width == 0
        and height == 0
        and color == 'red'
        and emphasis == 'strong'
        or highlight > 100):
        raise ValueError("sorry, you lose")

My preference is to actually break that logic up and avoid the wrapping in the first place, as in [2]. Which in this particular class has the side benefit of that value being used again in the same function anyways.

I'm starting to realize that Brandon Rhodes really had a big impact on my ideas of styling as I've been learning Python these past few years, as this was another one style I'm stealing from that same talk [3].

I've updated the PEP...

Great, thanks! I've created a ticket in pycodestyle [4] to update the style checker, which in turn will fix the flake8 error downstream once I get around (hopefully before PyCon) to releasing pycodestyle 1.8.0

[1] python/peps@master...IanLee1521:bpo-26763
[2] python/peps@0c790e7
[3] http://rhodesmill.org/brandon/slides/2012-11-pyconca/#naming-intermediate-values
[4] PyCQA/pycodestyle#498