isort 7.0.0 is no longer compatible with black 26.1.0

[felixfontein]

Black 26.1.0 got released earlier today, and adjusts some formatting related to imports.

Now if you format with both isort (in black mode) and black, each of the tools will change the other tool's output.

For example, isort:

--- a/noxfile.py
+++ b/noxfile.py
@@ -13,6 +13,7 @@ from pathlib import Path
 
 import nox
 
+
 try:
     import antsibull_nox
     import antsibull_nox.sessions

while black changes that back.

In another project, I also saw isort changing:

--- a/tests/unit/plugins/plugin_utils/test_inventory_filter.py
+++ b/tests/unit/plugins/plugin_utils/test_inventory_filter.py
@@ -4,6 +4,7 @@
 
 from __future__ import absolute_import, division, print_function
 
+
 __metaclass__ = type
 
 

while black changing that back.

There might be more differences, these are the ones I saw so far.

[cobaltt7]

Hey, Black maintainer here

How odd... we run both Black and isort on Black itself, so if there was an incompatibility, I believe we should've been able to notice it before this change was implemented

Could you share your exact Black and isort versions and config?

[felixfontein]

When looking closer, I saw that for isort we were setting lines_after_imports = 2, which at least in the past was required for black compatibility. This is apparently no longer needed. In any case, here's how I can reproduce this (I'm running it with Python 3.14):

$ pip list
Package         Version
--------------- -------
black           26.1.0
click           8.3.1
isort           7.0.0
mypy_extensions 1.1.0
packaging       25.0
pathspec        1.0.3
pip             25.3
platformdirs    4.5.1
pytokens        0.3.0

isort.cfg:

[isort]
profile=black
lines_after_imports = 2

t.py:

from __future__ import absolute_import, division, print_function


__metaclass__ = type

import nox


try:
    import antsibull_nox
    import antsibull_nox.sessions
except ImportError:
    pass

Commands:

isort --settings-file isort.cfg t.py
black t.py

So it looks like this is more a breaking change in black.

[cobaltt7]

Yes, as the first release in the year, 26.1.0 includes breaking changes and stabilizes the code style for 2026. See our stability policy for more information.

In the past, Black enforced "at least one" blank line after imports. Now, for better consistency, we enforce "exactly one" blank lines. See psf/black#2020 for more details.

So yes, lines_after_imports=2 is no longer needed. Since lines_after_imports=1 is the default, and manually setting it overrides the profile, I don't think it would make sense for isort to add it to the Black profile.

[felixfontein]

Thanks for explaining that! I didn't mean that 26.1.0 shouldn't have breaking changes, only that the thing I'm experiencing is caused by a breaking change in black.

In any case, it's good to know that I can now reduce my isort config by half by removing the lines_after_imports = 2 line :)

Closing since this isn't a problem in isort (and not one in black either). I probably would have noticed this earlier if I hadn't totally forgotten about the lines_after_imports = 2 line, I thought we only had profile=black in the isort config...

[DanielNoord]

Thanks for helping out here @cobalt7! Glas to see this was resolved :)