Latest black (25.1.0) adds a newline after docstring and before pass in an exception class

[simonw]

This file:

class ModelError(Exception):
    "Models can raise this error, which will be displayed to the user"
    pass

When run through the latest Black is reformatted to look like this:

class ModelError(Exception):
    "Models can raise this error, which will be displayed to the user"

    pass

Here's a way to see that happen using uvx. With the previous Black version:

echo 'class ModelError(Exception):
    "Models can raise this error, which will be displayed to the user"
    pass' | uvx --with 'black==24.10.0' black -

This outputs:

class ModelError(Exception):
    "Models can raise this error, which will be displayed to the user"
    pass
All done! ✨ 🍰 ✨
1 file left unchanged.

But if you bump to 25.1.0 this happens:

echo 'class ModelError(Exception):
    "Models can raise this error, which will be displayed to the user"
    pass' | uvx --with 'black==25.1.0' black - 

Output:

class ModelError(Exception):
    "Models can raise this error, which will be displayed to the user"

    pass
reformatted -

All done! ✨ 🍰 ✨
1 file reformatted.

[JelleZijlstra]

This is correct and expected. Black 25 releases our new stable style for 2025, and one of the thing it changes is a bugfix where we were previously failing to recognize strings like this one as docstrings. We previously already behaved this way for triple-quoted docstrings; now the behavior is consistent.

$ echo 'class ModelError(Exception):
    """Models can raise this error, which will be displayed to the user"""
    pass' | uvx --with 'black==25.1.0' black - --diff
--- STDIN	2025-01-31 20:34:18.575891+00:00
+++ STDOUT	2025-01-31 20:34:18.576843+00:00
@@ -1,3 +1,4 @@
 class ModelError(Exception):
     """Models can raise this error, which will be displayed to the user"""
+
     pass
would reformat -

All done! ✨ 🍰 ✨
1 file would be reformatted.
$ echo 'class ModelError(Exception):
    """Models can raise this error, which will be displayed to the user"""
    pass' | uvx --with 'black==24.10.0' black - --diff
--- STDIN	2025-01-31 20:34:23.106368+00:00
+++ STDOUT	2025-01-31 20:34:23.110604+00:00
@@ -1,3 +1,4 @@
 class ModelError(Exception):
     """Models can raise this error, which will be displayed to the user"""
+
     pass
would reformat -

All done! ✨ 🍰 ✨
1 file would be reformatted.

If you don't want the blank line, I'd recommend removing the pass; it's not needed.

[simonw]

Thanks for the explanation, that makes sense - I'll re-train myself not to use pass when i have an exception with a docstring like that.