What is PEP8's E128: continuation line under-i

Question

Just opened a file with Sublime Text (with Sublime Linter) and noticed a PEP8 formatting error that I'd never seen before. Here's the text:

urlpatterns = patterns('',
    url(r'^$', listing, name='investment-listing'),
)

It's flagging the second argument, the line that starts url(...)

I was about to disable this check in ST2 but I'd like to know what I'm doing wrong before I ignore it. You never know, if it seems important I might even change my ways :)

Answer 1

This goes also for statements like this (auto-formatted by PyCharm):

    return combine_sample_generators(sample_generators['train']), \
           combine_sample_generators(sample_generators['dev']), \
           combine_sample_generators(sample_generators['test'])

Which will give the same style-warning. In order to get rid of it I had to rewrite it to:

    return \
        combine_sample_generators(sample_generators['train']), \
        combine_sample_generators(sample_generators['dev']), \
        combine_sample_generators(sample_generators['test'])

Answer 2

PEP-8 recommends you indent lines to the opening parentheses if you put anything on the first line, so it should either be indenting to the opening bracket:

urlpatterns = patterns('',
                       url(r'^$', listing, name='investment-listing'))

or not putting any arguments on the starting line, then indenting to a uniform level:

urlpatterns = patterns(
    '',
    url(r'^$', listing, name='investment-listing'),
)

urlpatterns = patterns(
    '', url(r'^$', listing, name='investment-listing'))

I suggest taking a read through PEP-8 - it's not a long document, and it's pretty easy to understand, unlike some of the more technical PEPs.