What is the difference between B950 and max-line-length=88?

I see that black recommends the following flake8 configuration:

[flake8]
max-line-length = 80
...
select = C,E,F,W,B,B950
ignore = E501

However, the same thing can be achieved with the following configuration, which is shorter and possibly more explicit:

[flake8]
max-line-length = 88
...
select = C,E,F,W,B

Can you please help me understand why we need B950, then?

Thank you for flake8-bugbear!

[ambv]

Oh. Now I see what you are actually asking for. Sorry.

The rationale behind B950 is also explained in the README. It’s meant to be a soft warning, highway-speed style. If you go over less than 10% then it’s just a distraction to slow you down and get you to bow to the Line Length Demigod.

In other words, if your project’s style says: “we want line length to be 80”, then set “–line-length=80”. If you use E501 and then flake8 will stop and yell at you if you make a line 81 characters long. If you use B950, it will only stop you if you go over 88 characters.

It might be a weird thing but the intent is for it to be more humane. If you are driving 5 km/h over the speed limit of 90 km/h, police will not stop you, it’s not worth it for either of you. But you don’t change the speed limit to 95 km/h. People would start going over that, too. If you are at a conference and you do a talk and go over 2 minutes in your 30 minute-long keynote, people will not drag you from the stage. It’s not worth it for either of you. But you don’t change the length of the keynote to be 32 minutes long. People would start going over that, too. And so on, and so on.

I hope this clears it up.

[pquentin]

(Note that the url does not answer my question, since I was not asking how to enable B950, I was asking why it exists since it’s possible to get the same behavior without B950.)