Reformat code to comply with the Black 2024 Code Style.

[pkoz]

Motivation

The black library released a new version that implements the 2024 stable style.

It breaks tests because the black dependency in pyproject.toml has no constraint on the version.

Suggestion

• Quick fix: add the version constraint

optuna/pyproject.toml

Lines 53 to 55 in 073abfc

	checking = [
	"black",
	"blackdoc",

to:

checking = [
    "black<24.0.0"
    "blackdoc",

• Actual fix: reformat about 30 lines of code to comply with the Black 2024 Code Style.

Additional context (optional)

No response

[nzw0301]

Thank you for reporting it. When I used the latest black I encountered the following issues:

• additional newline added to docstring when the previous line length is less than the line length limit minus 1 psf/black#4180
• Black and flake8 no longer in sync psf/black#4173

Thus the proposed hotfix sounds nice.