Handle inline comments for imports

[Bengt]

Sometimes it is useful to comment imports, e.g. to clarify renames:

from a import f as f_small  # more space efficient implementation
from b import f as f_quick  # more time efficient implementation

Currently isort removes such inline comments:

from a import f as f_small
from b import f as f_quick

isort should reorder and reformat inline comments properly.

[timothycrosley]

Agreed,

historically isort hasn't done this because it adds a lot more complexity.

For instance given:

from a import b # comment 1
from a import c # comment 2

Considering the imports end up as:

from a import b, c

Where should the comments go? And what about dealing with line length limits etc?
However, I think at this stage of the project - it's worth it to make sure this works as best as possible:

from a import b, c # comment 1, comment 2

is after all, much better then stripping potentially useful comments.

Thank you for bringing this up, will fix and then deploy a new release.

~Tim

[Bengt]

Glad you see it that way. I see the complexity of this, which gets worse with the various multi-line modes. I think though, comments in imports are fairly common, so handling them seems worth an effort.

Yes, concatenating comments seems to be the best possible solution. That way no comments get lost and the user can edit them manually, if necessary. Concatenating with a comma might lead to ambiguity when the comments already contain commas:

from a import b  # bar, foos a foobar
from a import f  # foo, bars a foobar

That would become:

from a import b, f  # bar, foos a foobar, foo, bars a foobar

Maybe better use a semicolon, as it is far less commonly used:

from a import b, f  # bar, foos a foobar; foo, bars a foobar

[timothycrosley]

@Bengt, you're right a comma is too overused in comments to use as a separator here. I'll switch to a semicolon as suggested, thanks for pointing this out!

~Tim

[timothycrosley]

Fixed in version 3.6.0 :)

[Bengt]

Thanks for implementing this. It works almost as expected. I opened an issue for the remaining detail. See #129.

[dandavison]

Going back to the original example,

from a import f as f_small  # more space efficient implementation
from b import f as f_quick  # more time efficient implementation

If the user has specified --force_single_line_imports then these lines should simply be reordered, maintaining comments. Currently however, the comments are completely lost. I'd like to suggest re-opening this issue to address that problem.

[dandavison]

Sorry, the above comment was slightly inaccurate. In fact, this is not an issue with --force_single_line_imports; this is an issue with the default behavior:

from a import b  # b comment
from a import c  # c comment

is left unchanged, whereas

from a import b as bb  # b comment
from a import c as cc  # c comment

has its comments stripped.

[dandavison]

I've proposed a fix for the above issue in PR #179.