Formatting list comprehensions

[hayd]

My suggestion is the following:

1. break in expression* => break the for and the if (edit: this is implied by 2.).
2. break the for => break the if.

*This should add a continued_indent.

.1. seems obvious to me, I can see 2. being slightly more controversial...

To give a silly example:

# current
["This is a list comprehension which is quite long, I want it to split" +
 "a second long string pushes this over 79" for i in range(3) if i == 1]

# one possible
["This is a list comprehension which is quite long, I want it to split" +
     "a second long string pushes this over 79"
 for i in range(3) if i == 1]

# my suggestion
["This is a list comprehension which is quite long, I want it to split" +
     "a second long string pushes this over 79"
 for i in range(3)
 if i == 1]

# autopep8
["This is a list comprehension which is quite long, I want it to split" +
    "a second long string pushes this over 79" for i in range(3) if i == 1]

I realise @gwelymernans is working on list comprehensions, but thought I should punt this as an issue.

[bwendling]

It's not a bad heuristic, I think. Though figuring out if there's a break in the expression might be complicated. The current way to figure out if a split occurred previous to the list comprehension is to backtrack through the tokens to find a split, which is sucky behavior if not done carefully.

[slippycheeze]

FWIW, I'd strongly prefer to be able to break before the "for" and "if" statements in a list comprehension, even if they could be packed to a single line, unless the whole thing fits on a single line. (and even then, I prefer separating them, because it matches better the "one statement per line" model of Python code, IMO, but I realise that's personal taste related.)

[msuozzo]

I think #470 may have introduced options to fix this.

I'd strongly prefer to be able to break before the "for" and "if" statements in a list comprehension

SPLIT_COMPLEX_COMPREHENSION should satisfy this preference.