Black

Highlights

- Add support for the new Python 3.12 f-string syntax introduced by PEP 701 (3822)

Stable style

- Fix crash involving indented dummy functions containing newlines (4318)

Parser

- Add support for type parameter defaults, a new syntactic feature added to Python 3.13
by PEP 696 (4327)

Integrations

- Github Action now works even when `git archive` is skipped (4313)

Stable style

- Fix unwanted crashes caused by AST equivalency check (4290)

Preview style

- `if` guards in `case` blocks are now wrapped in parentheses when the line is too long.
(4269)
- Stop moving multiline strings to a new line unless inside brackets (4289)

Integrations

- Add a new option `use_pyproject` to the GitHub Action `psf/black`. This will read the
Black version from `pyproject.toml`. (4294)

Highlights

This release is a milestone: it fixes Black's first CVE security vulnerability. If you
run Black on untrusted input, or if you habitually put thousands of leading tab
characters in your docstrings, you are strongly encouraged to upgrade immediately to fix
[CVE-2024-21503](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-21503).

This release also fixes a bug in Black's AST safety check that allowed Black to make
incorrect changes to certain f-strings that are valid in Python 3.12 and higher.

Stable style

- Don't move comments along with delimiters, which could cause crashes (4248)
- Strengthen AST safety check to catch more unsafe changes to strings. Previous versions
of Black would incorrectly format the contents of certain unusual f-strings containing
nested strings with the same quote type. Now, Black will crash on such strings until
support for the new f-string syntax is implemented. (4270)
- Fix a bug where line-ranges exceeding the last code line would not work as expected
(4273)

Performance

- Fix catastrophic performance on docstrings that contain large numbers of leading tab
characters. This fixes
[CVE-2024-21503](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-21503).
(4278)

Documentation

- Note what happens when `--check` is used with `--quiet` (4236)

Stable style

- Fixed a bug where comments where mistakenly removed along with redundant parentheses
(4218)

Preview style

- Move the `hug_parens_with_braces_and_square_brackets` feature to the unstable style
due to an outstanding crash and proposed formatting tweaks (4198)
- Fixed a bug where base expressions caused inconsistent formatting of \*\* in tenary
expression (4154)
- Checking for newline before adding one on docstring that is almost at the line limit
(4185)
- Remove redundant parentheses in `case` statement `if` guards (4214).

Configuration

- Fix issue where _Black_ would ignore input files in the presence of symlinks (4222)
- _Black_ now ignores `pyproject.toml` that is missing a `tool.black` section when
discovering project root and configuration. Since _Black_ continues to use version
control as an indicator of project root, this is expected to primarily change behavior
for users in a monorepo setup (desirably). If you wish to preserve previous behavior,
simply add an empty `[tool.black]` to the previously discovered `pyproject.toml`
(4204)

Output

- Black will swallow any `SyntaxWarning`s or `DeprecationWarning`s produced by the `ast`
module when performing equivalence checks (4189)

Integrations

- Add a JSONSchema and provide a validate-pyproject entry-point (4181)

Bugfix release to fix a bug that made Black unusable on certain file systems with strict
limits on path length.

Preview style

- Consistently add trailing comma on typed parameters (4164)

Configuration

- Shorten the length of the name of the cache file to fix crashes on file systems that
do not support long paths (4176)

Highlights

This release introduces the new 2024 stable style (4106), stabilizing the following
changes:

- Add parentheses around `if`-`else` expressions (2278)
- Dummy class and function implementations consisting only of `...` are formatted more
compactly (3796)
- If an assignment statement is too long, we now prefer splitting on the right-hand side
(3368)
- Hex codes in Unicode escape sequences are now standardized to lowercase (2916)
- Allow empty first lines at the beginning of most blocks (3967, 4061)
- Add parentheses around long type annotations (3899)
- Enforce newline after module docstrings (3932, 4028)
- Fix incorrect magic trailing comma handling in return types (3916)
- Remove blank lines before class docstrings (3692)
- Wrap multiple context managers in parentheses if combined in a single `with` statement
(3489)
- Fix bug in line length calculations for power operations (3942)
- Add trailing commas to collection literals even if there's a comment after the last
entry (3393)
- When using `--skip-magic-trailing-comma` or `-C`, trailing commas are stripped from
subscript expressions with more than 1 element (3209)
- Add extra blank lines in stubs in a few cases (3564, 3862)
- Accept raw strings as docstrings (3947)
- Split long lines in case blocks (4024)
- Stop removing spaces from walrus operators within subscripts (3823)
- Fix incorrect formatting of certain async statements (3609)
- Allow combining ` fmt: skip` with other comments (3959)

There are already a few improvements in the `--preview` style, which are slated for the
2025 stable style. Try them out and
[share your feedback](https://github.com/psf/black/issues). In the past, the preview
style has included some features that we were not able to stabilize. This year, we're
adding a separate `--unstable` style for features with known problems. Now, the
`--preview` style only includes features that we actually expect to make it into next
year's stable style.

Stable style

Several bug fixes were made in features that are moved to the stable style in this
release:

- Fix comment handling when parenthesising conditional expressions (4134)
- Fix bug where spaces were not added around parenthesized walruses in subscripts,
unlike other binary operators (4109)
- Remove empty lines before docstrings in async functions (4132)
- Address a missing case in the change to allow empty lines at the beginning of all
blocks, except immediately before a docstring (4130)
- For stubs, fix logic to enforce empty line after nested classes with bodies (4141)

Preview style

- Add `--unstable` style, covering preview features that have known problems that would
block them from going into the stable style. Also add the `--enable-unstable-feature`
flag; for example, use
`--enable-unstable-feature hug_parens_with_braces_and_square_brackets` to apply this
preview feature throughout 2024, even if a later Black release downgrades the feature
to unstable (4096)
- Format module docstrings the same as class and function docstrings (4095)
- Fix crash when using a walrus in a dictionary (4155)
- Fix unnecessary parentheses when wrapping long dicts (4135)
- Stop normalizing spaces before ` fmt: skip` comments (4146)

Configuration

- Print warning when configuration in `pyproject.toml` contains an invalid key (4165)
- Fix symlink handling, properly ignoring symlinks that point outside of root (4161)
- Fix cache mtime logic that resulted in false positive cache hits (4128)
- Remove the long-deprecated `--experimental-string-processing` flag. This feature can
currently be enabled with `--preview --enable-unstable-feature string_processing`.
(4096)

Integrations

- Revert the change to run Black's pre-commit integration only on specific git hooks
(3940) for better compatibility with older versions of pre-commit (4137)