Simon Willison’s Weblog

Latest black (25.1.0) adds a newline after docstring and before pass in an exception class. I filed a bug report against Black when the latest release - 25.1.0 - reformatted the following code to add an ugly (to me) newline between the docstring and the pass:

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

    pass

Black maintainer Jelle Zijlstra confirmed that this is intended behavior with respect to Black's 2025 stable style, but also helped me understand that the pass there is actually unnecessary so I can fix the aesthetics by removing that entirely.

I'm linking to this issue because it's a neat example of how I like to include steps-to-reproduce using uvx to create one-liners you can paste into a terminal to see the bug that I'm reporting. In this case I shared the following:

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.

Via David Szotten I learned that you can use uvx black@25.1.0 here instead.