The python black project.

Slawomir Kaplonski skaplons at
Thu Apr 18 11:02:10 UTC 2019


> Wiadomość napisana przez Stephen Finucane <sfinucan at> w dniu 18.04.2019, o godz. 12:33:
> On Thu, 2019-04-18 at 11:56 +0200, Dmitry Tantsur wrote:
>> On 4/18/19 11:52 AM, Sorin Sbarnea wrote:
>>> Black is a python code formatter, something similar to the older
>>> yapf.
>>> I do like to avoid discussions about formatting in code reviews and
>>> prefer to let the linter take care of what could count as
>>> appointed.
>> That's what pep8 jobs are for. They cannot be replaced with a pre-
>> commit hooks, because people who are mostly likely to screw up
>> formatting are also most likely to not have it installed.
>>> My experience with yapf was far from idea as they decided to change
>>> formatting in a major way in their last *minor* version update,
>>> breaking havoc.
>>> There is one reason why I did not even try black: it does require
>>> python3.6 !!!
>>> While I do have a huge range of python version installed on my own
>>> dev machines, I cannot say the same about the average
>>> developer/contributor.
>>> Considering that on CentOS-7 you can only get python3.5... this
>>> rest my case.
>> You're welcome: 
>> :)
> You've also got tox and virtualenvs in general, but I don't think this
> is a serious issue tbh...
>>> I do not want to limit the number of platform for contributors on
>>> any project, especially when we talk about one of the most
>>> basic/early check a developer would have to run on any change they
>>> make.
>>> That is why -1 on black, and I guess it will be like this until we
>>> have CentOS 8 released. On the other hand, about yapf use I have
>>> mixed feelings.
>>> I would rather prefer to see better adoption/coverage of: flake8,
>>> ansible-lint and yamllint -- preferably orchestrated via pre-commit 
>>> as it lowers the execution time and disk footprint (sharing/caching
>>> identical linters between repositories) -- opposed to tox which
>>> does not shared anything between repositories. Tripleo-quickstart
>>> and tripleo-ci repositories are already using it and I did not hear
>>> many complaints, other than having to explain that pre-commit is
>>> does not require the use of a git hook.
>> I think we already use flake8 openstack-wide, what will Black bring
>> us in addition to that?
> I've seen this used with packages such as tox and warehouse (the new
> code base for black is intended to be an opinionated code
> formatter and exposes no knobs to the user, meaning it's very much
> "their way or the highway". This makes it different from something like
> yapf, which exposes all these knobs and therefore allows for arguments
> about e.g. whether one should use single or double quotes. No
> configuration knobs means no ability to discuss these preferences,
> which for something as subjective as code formatting seems to be a good
> thing to me.
> Now, as to whether it's practical, you have to realize that for it to
> be of any use, black has to be run initially over your entire codebase
> and then rerun on each commit. The latter isn't an issue (we already
> run flake8 for this purpose) but I genuinely cannot see something like
> nova rewrapping every line of code (all 552,347 of them, if my quick
> check is correct), essentially breaking the ability to cleanly backport
> patches and get meaningful 'git blame' output simply to avoid the
> occasional debate about code formatting. I think adopting black for a
> _new_ project (or even a very small one) could be a great idea, but for
> something as large and cumbersome as nova (or neutron, glance, cinder,
> some of the oslo libraries, etc.), maaaaaybe not.

+100 to this. Resolving manually many conflicts between master and stable branches just because e.g. quoting was changed doesn’t seems like good thing :)

> Stephen
> PS: As an aside, I would like to see something like black provided as
> part of the Python standard library to settle formatting issues for
> once and for all and help ensure that a minimum standard is set for
> most code you'll find (though code quality covers far more than mere
> formatting). To the best of my knowledge, the gofmt tool in go(lang)
> fills this role but I really can't see that happening within Python any
> time soon.
>> Dmitry
>>> Shortly, +2 on more pre-commit use, the tool not the git hook.
>>> PS. Please do not bring the SCL into the thread, they do not
>>> provide a single command enablement of additional python
>>> interpreters (not in PATH).
>>>> On 18 Apr 2019, at 09:57, Dmitry Tantsur <dtantsur at>
>>>> wrote:
>>>> Hi,
>>>> On 4/18/19 10:51 AM, Natal Ngétal wrote:
>>>>> Hi everyone,
>>>>> Black is project to format Python code. It's more and more used
>>>>> by the python community. That can save time and harmonize the
>>>>> code. For example, simple quote versus double quote, that was
>>>>> not checked by pep8.i It's just an example of what make  black
>>>>> With a pre-hook commit hook this will be also avoid to lose
>>>>> time with pep8 errors.
>>>> I'm not sure what exactly Black does, but the last thing I want
>>>> to see is patches changing between single and double quotes. If
>>>> it's not the case or it can be turned off, I'm all for
>>>> experimenting.
>>>>> Two links to see more:
>>>>> I think it can be very interesting to start to use Black on
>>>>> OpenStack. What do you thinks about that? For example, we can
>>>>> introduce it on some projects, I would volunteer to try on
>>>>> TripleO.
>>>> Given it's a pre-commit hook, isn't it supposed to be done on
>>>> developer's machines? If so, how do you see applying Black to the
>>>> whole OpenStack?
>>>> Dmitry
>>>>> My best regards

Slawek Kaplonski
Senior software engineer
Red Hat

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