Cercis

Highlights

This is the first release of 2023, and following our
[stability policy](https://black.readthedocs.io/en/stable/the_black_code_style/index.html#stability-policy),
it comes with a number of improvements to our stable style, including improvements to
empty line handling, removal of redundant parentheses in several contexts, and output
that highlights implicitly concatenated strings better.

There are also many changes to the preview style; try out `black --preview` and give us
feedback to help us set the stable style for next year.

In addition to style changes, Black now automatically infers the supported Python
versions from your `pyproject.toml` file, removing the need to set Black's target
versions separately.

Stable style

<!-- Changes that affect Black's stable style -->

- Introduce the 2023 stable style, which incorporates most aspects of last year's
preview style (3418). Specific changes:
- Enforce empty lines before classes and functions with sticky leading comments
(3302) (22.12.0)
- Reformat empty and whitespace-only files as either an empty file (if no newline is
present) or as a single newline character (if a newline is present) (3348)
(22.12.0)
- Implicitly concatenated strings used as function args are now wrapped inside
parentheses (3307) (22.12.0)
- Correctly handle trailing commas that are inside a line's leading non-nested parens
(3370) (22.12.0)
- `--skip-string-normalization` / `-S` now prevents docstring prefixes from being
normalized as expected (3168) (since 22.8.0)
- When using `--skip-magic-trailing-comma` or `-C`, trailing commas are stripped from
subscript expressions with more than 1 element (3209) (22.8.0)
- Implicitly concatenated strings inside a list, set, or tuple are now wrapped inside
parentheses (3162) (22.8.0)
- Fix a string merging/split issue when a comment is present in the middle of
implicitly concatenated strings on its own line (3227) (22.8.0)
- Docstring quotes are no longer moved if it would violate the line length limit
(3044, 3430) (22.6.0)
- Parentheses around return annotations are now managed (2990) (22.6.0)
- Remove unnecessary parentheses around awaited objects (2991) (22.6.0)
- Remove unnecessary parentheses in `with` statements (2926) (22.6.0)
- Remove trailing newlines after code block open (3035) (22.6.0)
- Code cell separators `%%` are now standardised to ` %%` (2919) (22.3.0)
- Remove unnecessary parentheses from `except` statements (2939) (22.3.0)
- Remove unnecessary parentheses from tuple unpacking in `for` loops (2945) (22.3.0)
- Avoid magic-trailing-comma in single-element subscripts (2942) (22.3.0)
- Fix a crash when a colon line is marked between ` fmt: off` and ` fmt: on` (3439)

Preview style

<!-- Changes that affect Black's preview style -->

- Format hex codes in unicode escape sequences in string literals (2916)
- Add parentheses around `if`-`else` expressions (2278)
- Improve performance on large expressions that contain many strings (3467)
- Fix a crash in preview style with assert + parenthesized string (3415)
- Fix crashes in preview style with walrus operators used in function return annotations
and except clauses (3423)
- Fix a crash in preview advanced string processing where mixed implicitly concatenated
regular and f-strings start with an empty span (3463)
- Fix a crash in preview advanced string processing where a standalone comment is placed
before a dict's value (3469)
- Fix an issue where extra empty lines are added when a decorator has ` fmt: skip`
applied or there is a standalone comment between decorators (3470)
- Do not put the closing quotes in a docstring on a separate line, even if the line is
too long (3430)
- Long values in dict literals are now wrapped in parentheses; correspondingly
unnecessary parentheses around short values in dict literals are now removed; long
string lambda values are now wrapped in parentheses (3440)
- Fix two crashes in preview style involving edge cases with docstrings (3451)
- Exclude string type annotations from improved string processing; fix crash when the
return type annotation is stringified and spans across multiple lines (3462)
- Wrap multiple context managers in parentheses when targeting Python 3.9+ (3489)
- Fix several crashes in preview style with walrus operators used in `with` statements
or tuples (3473)
- Fix an invalid quote escaping bug in f-string expressions where it produced invalid
code. Implicitly concatenated f-strings with different quotes can now be merged or
quote-normalized by changing the quotes used in expressions. (3509)
- Fix crash on `await (yield)` when Black is compiled with mypyc (3533)

Configuration

<!-- Changes to how Black can be configured -->

- Black now tries to infer its `--target-version` from the project metadata specified in
`pyproject.toml` (3219)

Packaging

<!-- Changes to how Black is packaged, such as dependency requirements -->

- Upgrade mypyc from `0.971` to `0.991` so mypycified _Black_ can be built on armv7
(3380)
- This also fixes some crashes while using compiled Black with a debug build of
CPython
- Drop specific support for the `tomli` requirement on 3.11 alpha releases, working
around a bug that would cause the requirement not to be installed on any non-final
Python releases (3448)
- Black now depends on `packaging` version `22.0` or later. This is required for new
functionality that needs to parse part of the project metadata (3219)

Output

<!-- Changes to Black's terminal output and error messages -->

- Calling `black --help` multiple times will return the same help contents each time
(3516)
- Verbose logging now shows the values of `pyproject.toml` configuration variables
(3392)
- Fix false symlink detection messages in verbose output due to using an incorrect
relative path to the project root (3385)

Integrations

<!-- For example, Docker, GitHub Actions, pre-commit, editors -->

- Move 3.11 CI to normal flow now that all dependencies support 3.11 (3446)
- Docker: Add new `latest_prerelease` tag automation to follow latest black alpha
release on docker images (3465)

Documentation

<!-- Major changes to documentation and policies. Small docs changes
don't need a changelog entry. -->

- Expand `vim-plug` installation instructions to offer more explicit options (3468)

Preview style

<!-- Changes that affect Black's preview style -->

- Enforce empty lines before classes and functions with sticky leading comments (3302)
- Reformat empty and whitespace-only files as either an empty file (if no newline is
present) or as a single newline character (if a newline is present) (3348)
- Implicitly concatenated strings used as function args are now wrapped inside
parentheses (3307)
- For assignment statements, prefer splitting the right hand side if the left hand side
fits on a single line (3368)
- Correctly handle trailing commas that are inside a line's leading non-nested parens
(3370)

Configuration

<!-- Changes to how Black can be configured -->

- Fix incorrectly applied `.gitignore` rules by considering the `.gitignore` location
and the relative path to the target file (3338)
- Fix incorrectly ignoring `.gitignore` presence when more than one source directory is
specified (3336)

Parser

<!-- Changes to the parser or to version autodetection -->

- Parsing support has been added for walruses inside generator expression that are
passed as function args (for example,
`any(match := my_re.match(text) for text in texts)`) (3327).

Integrations

<!-- For example, Docker, GitHub Actions, pre-commit, editors -->

- Vim plugin: Optionally allow using the system installation of Black via
`let g:black_use_virtualenv = 0`(3309)

Highlights

- Runtime support for Python 3.6 has been removed. Formatting 3.6 code will still be
supported until further notice.

Stable style

- Fix a crash when ` fmt: on` is used on a different block level than ` fmt: off`
(3281)

Preview style

- Fix a crash when formatting some dicts with parenthesis-wrapped long string keys
(3262)

Configuration

- `.ipynb_checkpoints` directories are now excluded by default (3293)
- Add `--skip-source-first-line` / `-x` option to ignore the first line of source code
while formatting (3299)

Packaging

- Executables made with PyInstaller will no longer crash when formatting several files
at once on macOS. Native x86-64 executables for macOS are available once again.
(3275)
- Hatchling is now used as the build backend. This will not have any effect for users
who install Black with its wheels from PyPI. (3233)
- Faster compiled wheels are now available for CPython 3.11 (3276)

_Blackd_

- Windows style (CRLF) newlines will be preserved (3257).

Integrations

- Vim plugin: add flag (`g:black_preview`) to enable/disable the preview style (3246)
- Update GitHub Action to support formatting of Jupyter Notebook files via a `jupyter`
option (3282)
- Update GitHub Action to support use of version specifiers (e.g. `<23`) for Black
version (3265)

Highlights

- Python 3.11 is now supported, except for _blackd_ as aiohttp does not support 3.11 as
of publishing (3234)
- This is the last release that supports running _Black_ on Python 3.6 (formatting 3.6
code will continue to be supported until further notice)
- Reword the stability policy to say that we may, in rare cases, make changes that
affect code that was not previously formatted by _Black_ (3155)

Stable style

- Fix an infinite loop when using ` fmt: on/off` in the middle of an expression or code
block (3158)
- Fix incorrect handling of ` fmt: skip` on colon (`:`) lines (3148)
- Comments are no longer deleted when a line had spaces removed around power operators
(2874)

Preview style

- Single-character closing docstring quotes are no longer moved to their own line as
this is invalid. This was a bug introduced in version 22.6.0. (3166)
- `--skip-string-normalization` / `-S` now prevents docstring prefixes from being
normalized as expected (3168)
- When using `--skip-magic-trailing-comma` or `-C`, trailing commas are stripped from
subscript expressions with more than 1 element (3209)
- Implicitly concatenated strings inside a list, set, or tuple are now wrapped inside
parentheses (3162)
- Fix a string merging/split issue when a comment is present in the middle of implicitly
concatenated strings on its own line (3227)

_Blackd_

- `blackd` now supports enabling the preview style via the `X-Preview` header (3217)

Configuration

- Black now uses the presence of debug f-strings to detect target version (3215)
- Fix misdetection of project root and verbose logging of sources in cases involving
`--stdin-filename` (3216)
- Immediate `.gitignore` files in source directories given on the command line are now
also respected, previously only `.gitignore` files in the project root and
automatically discovered directories were respected (3237)

Documentation

- Recommend using BlackConnect in IntelliJ IDEs (3150)

Integrations

- Vim plugin: prefix messages with `Black: ` so it's clear they come from Black (3194)
- Docker: changed to a /opt/venv installation + added to PATH to be available to
non-root users (3202)

Output

- Change from deprecated `asyncio.get_event_loop()` to create our event loop which
removes DeprecationWarning (3164)
- Remove logging from internal `blib2to3` library since it regularly emits error logs
about failed caching that can and should be ignored (3193)

Parser

- Type comments are now included in the AST equivalence check consistently so accidental
deletion raises an error. Though type comments can't be tracked when running on PyPy
3.7 due to standard library limitations. (2874)

Performance

- Reduce Black's startup time when formatting a single file by 15-30% (3211)

Style

- Fix unstable formatting involving `fmt: skip` and ` fmt:skip` comments (notice the
lack of spaces) (2970)

Preview style

- Docstring quotes are no longer moved if it would violate the line length limit (3044)
- Parentheses around return annotations are now managed (2990)
- Remove unnecessary parentheses around awaited objects (2991)
- Remove unnecessary parentheses in `with` statements (2926)
- Remove trailing newlines after code block open (3035)

Integrations

- Add `scripts/migrate-black.py` script to ease introduction of Black to a Git project
(3038)

Output

- Output Python version and implementation as part of `--version` flag (2997)

Packaging

- Use `tomli` instead of `tomllib` on Python 3.11 builds where `tomllib` is not
available (2987)

Parser

- [PEP 654](https://peps.python.org/pep-0654/#except) syntax (for example,
`except *ExceptionGroup:`) is now supported (3016)
- [PEP 646](https://peps.python.org/pep-0646) syntax (for example,
`Array[Batch, *Shape]` or `def fn(*args: *T) -> None`) is now supported (3071)

Vim Plugin

- Fix `strtobool` function. It didn't parse true/on/false/off. (3025)

Preview style

- Code cell separators `%%` are now standardised to ` %%` (2919)
- Remove unnecessary parentheses from `except` statements (2939)
- Remove unnecessary parentheses from tuple unpacking in `for` loops (2945)
- Avoid magic-trailing-comma in single-element subscripts (2942)

Configuration

- Do not format `__pypackages__` directories by default (2836)
- Add support for specifying stable version with `--required-version` (2832).
- Avoid crashing when the user has no homedir (2814)
- Avoid crashing when md5 is not available (2905)
- Fix handling of directory junctions on Windows (2904)

Documentation

- Update pylint config documentation (2931)

Integrations

- Move test to disable plugin in Vim/Neovim, which speeds up loading (2896)

Output

- In verbose mode, log when _Black_ is using user-level config (2861)

Packaging

- Fix Black to work with Click 8.1.0 (2966)
- On Python 3.11 and newer, use the standard library's `tomllib` instead of `tomli`
(2903)
- `black-primer`, the deprecated internal devtool, has been removed and copied to a
[separate repository](https://github.com/cooperlees/black-primer) (#2924)

Parser

- Black can now parse starred expressions in the target of `for` and `async for`
statements, e.g `for item in *items_1, *items_2: pass` (2879).