Style guide fix for W503 W504

[LefterisJP]

All of a sudden flake8 started reporting a W504 violation for our code due to us putting the line break after the operator in long expressions with operators that were broken in multiple lines.

This was introduced in the latest version of flake8 and made our code non flake8 compatible right under our noses.
I tried to change it to have the line break before the operator and then flake8 reported a W503 violation. Damned if you do, damned if you don't.

That looked fishy so I did some digging:
PyCQA/pycodestyle#498
PyCQA/pycodestyle#502

The W503 bug is already fixed as it’s added to the default ignore list but you have a ignore option configured in setup.cfg and if that’s the case the default ignores aren’t respected anymore. This is in my opinion pretty stupid behavior but a flake8 thing I can’t do anything about. That means though that if you specify a ignore list you have to list all default ignores as well. So I updated the list in setup.cfg and now the tests pass without problems.

Apparently this flake8 violation was considered opinionated and put in the default ignores. But there is a bug that if you have any ignores specified (which we do) then you lose all the default ignores.

Solution

Put W504to the ignores, so that flake8 reports correctly when we ever make a W503 violation. Add the rule that line breaks should come after the operator to the style guide.

Note: This rule also applies to solidity code.

[loredanacirstea]

@LefterisJP , why not just add W503 to setup.cfg and follow PEP 8?

Ah, you would have a lot of violations, therefore a lot of code to change. Ok.

[coveralls]

Coverage increased (+0.05%) to 62.749% when pulling 45fe431 on LefterisJP:style_guide_fix_W503_W504 into 108e0c3 on raiden-network:master.

[coveralls]

Coverage increased (+12.3%) to 74.963% when pulling 45fe431 on LefterisJP:style_guide_fix_W503_W504 into 108e0c3 on raiden-network:master.

[LefterisJP]

@loredanacirstea The good thing is that if we ever wanna change the style we just ignore W503 instead and flake8 will show us every violation that we need to address. Hopefully we won't do that soon though.