Black: Documentation: Comparison between Black and WPS

[DonaldTsang]

As https://github.com/wemake-services/wemake-python-styleguide/issues/1059 have noted
(and as https://wemake-python-stylegui.de/en/latest/pages/usage/integrations/auto-formatters.html#black have referenced), there are a few noticeable difference between Black and WeMake Python StyleGuide. Here are some questions:

• Is it possible to set line length maximums as 79/80 characters?
  
  
  
  • https://github.com/psf/black/blob/master/pyproject.toml#L9 is a possible answer?
  
  
• Is it possible to preserve trailing comma as a default setting?
• Is it possible to treat single quote as the standard instead of double quote?
• Is it possible to have black+WPS instead of autopep8+WPS as a standard?

[hugovk]

Black intentionally has very few options. See https://github.com/psf/black#command-line-options.

Is it possible to set line length maximums as 79/80 characters?

• /pyproject.toml@master#L9 is a possible answer?

Yes, see --line-length: https://github.com/psf/black#line-length

• Is it possible to treat single quote as the standard instead of double quote?

No, but you can use --skip-string-normalization to prevent changing existing singles to doubles. See https://github.com/psf/black#strings.

[DonaldTsang]

@hugovk what about preserving trailing commas in lists and objects (since that is a convention adopted by many projects)?

[hugovk]

If it's not in the documentation, then no.

I think there is a PR related to trailing commas, but I don't think there'll be an option.

[DonaldTsang]

@hugovk would like to see the PR exist though, since that would allow maximum compatibility with WPS, turning it into a powerhouse.

Also some have suggested that the max line length limit needs to be hardened (see https://github.com/wemake-services/wemake-python-styleguide/issues/518 and https://github.com/wemake-services/wemake-python-styleguide/issues/890 )

[ferdnyc]

It strikes me that https://wemake-python-stylegui.de/en/latest/pages/usage/integrations/auto-formatters.html#black is out of date, because according to the Black docs (emphasis mine):

Trailing commas

_Black_ will add trailing commas to expressions that are split by comma where each element is on its own line. This includes function signatures.

Unnecessary trailing commas are removed if an expression fits in one line. This makes it 1% more likely that your line won’t exceed the allotted line length limit. Moreover, in this scenario, if you added another argument to your call, you’d probably fit it in the same line anyway. That doesn’t make diffs any larger.

One exception to removing trailing commas is tuple expressions with just one element. In this case _Black_ won’t touch the single trailing comma as this would unexpectedly change the underlying data type. Note that this is also the case when commas are used while indexing. This is a tuple in disguise: numpy_array[3, ].

One exception to adding trailing commas is function signatures containing *, *args, or **kwargs. In this case a trailing comma is only safe to use on Python 3.6. _Black_ will detect if your file is already 3.6+ only and use trailing commas in this situation. If you wonder how it knows, it looks for f-strings and existing use of trailing commas in function signatures that have stars in them. In other words, if you’d like a trailing comma in this situation and _Black_ didn’t recognize it was safe to do so, put it there manually and _Black_ will keep it.

[DonaldTsang]

Is it possible to enforce trailing commas instead of removing them? Assuming that that are out-of-date and that we are trying to be WPS-compliant (since they stated that https://github.com/asottile/add-trailing-comma is perfect for WPS)? Also if you are free, is it possible for us to collaborate over at the Issue page in WPS?

[ferdnyc]

@DonaldTsang According to the add-trailing-comma readme, it does exactly the same thing as _Black_ for one-line lists:

remove unnecessary commas

yes yes, I realize the tool is called add-trailing-comma :laughing:

-[1, 2, 3,]
-[1, 2, 3, ]
+[1, 2, 3]
+[1, 2, 3]

[DonaldTsang]

@ferdnyc if you are free, is it possible for us to collaborate over at the Issue page in WPS?

Also @hugovk is it possible for us to "force" single quotes instead of just allowing single quotes? It should be simple to regex "'\"" => '\'"' where single quotes have their escapes removed and double quotes have escapes to go with them?

Have anyone tested this statment's validity yet?

black itself violates a lot of flake8 rules that this linter respects.

[hugovk]

Also @hugovk is it possible for us to "force" single quotes instead of just allowing single quotes? It should be simple to regex "'\"" => '\'"' where single quotes have their escapes removed and double quotes have escapes to go with them?

No, this has been discussed many times and it's unlikely Black will change.

You could use the double-quote-string-fixer pre-commit hook.

[ferdnyc]

@DonaldTsang The info I posted here is the same information (it turns out) that @uhbif19 included when opening wemake-services/wemake-python-styleguide#890 over two months ago. Seems to me the problem isn't that information is needed, it's that it needs to be acted on by someone involved in WPS. I have nothing more to add, really.

[DonaldTsang]

@hugovk is it possible to make the fixer a plugin to black or a separate program? Not everyone uses pre-commit hooks in their workflow.

[hugovk]

Not as a plugin to Black, but you can run pre-commit as a standalone tool without actually using installing the pre-commit hooks. See the CI in this repo, for example.

[ambv]

You can use --line-length= and -S. Preserving trailing commas will work consistently when #1288 is finished.

[DonaldTsang]

@ambv Can you confirm the edited documentation in https://hackmd.io/3vzJNofVQ_G0aS_QWwvLQA in case I make any errors?

Also to @ferdnyc there has been more discoveries with such incompatibilities https://github.com/wemake-services/wemake-python-styleguide/issues/890#issuecomment-555844089

[ferdnyc]

Please do not tag me on this issue, I have no desire to be involved any further.

[ichard26]

@DonaldTsang

And there’s no configuration to fix it!

This is partially true, the comments about _Black_'s usage of double quotes and unstable trailing comma enforcement are valid. What is not valid is the comment about line length. There is a way to configure it, it can be done via --line-length=80. I get that having to configure it can be annoying, but to imply that it is not configurable is misleading.

Also a slight nitpick, -S won't really fix the single quotes vs double quotes issue. For the foreseeable future, _Black_ will not be enforcing single quote usage. You can disable the auto-formatting of quotes via -S, but not configure the auto-formatting to enforce single quotes. Instead, I would recommend using a different tool to enforce single quotes.

[DonaldTsang]

@ichard26 I think I have redacted that specific line in the HackMD document prior to your comment. Other than that, I think that there might be tools to switching from enforcing single quotes to enforcing double quotes like "double-quote-string-fixer".

[ichard26]

@DonaldTsang, sorry about that, I was looking the version hosted at readthedocs since it looked better formatted and for other reasons... oops.. Anyway, technically it LGTM. Original comment about -S still stands though, it's more like a hack than a fix.