The Uncompromising Code Formatter

“Any color you like.”

Black is the uncompromising Python code formatter. By using it, you agree to cede control over minutiae of hand-formatting. In return, Black gives you speed, determinism, and freedom from pycodestyle nagging about formatting. You will save time and mental energy for more important matters.

Blackened code looks the same regardless of the project you're reading. Formatting becomes transparent after a while and you can focus on the content instead.

Black makes code review faster by producing the smallest diffs possible.

Try it out now using the Black Playground. Watch the PyCon 2019 talk to learn more.

Read the documentation on ReadTheDocs!

Installation and usage

Installation

Black can be installed by running pip install black. It requires Python 3.6.2+ to run. If you want to format Python 2 code as well, install with pip install black[python2].

If you can't wait for the latest hotness and want to install from GitHub, use:

pip install git+git://github.com/psf/black

Usage

To get started right away with sensible defaults:

black {source_file_or_directory}

You can run Black as a package if running it as a script doesn't work:

python -m black {source_file_or_directory}

Further information can be found in our docs:

• Usage and Configuration

NOTE: This is a beta product

Black is already successfully used by many projects, small and big. Black has a comprehensive test suite, with efficient parallel tests, and our own auto formatting and parallel Continuous Integration runner. However, Black is still beta. Things will probably be wonky for a while. This is made explicit by the "Beta" trove classifier, as well as by the "b" in the version number. What this means for you is that until the formatter becomes stable, you should expect some formatting to change in the future. That being said, no drastic stylistic changes are planned, mostly responses to bug reports.

Also, as a safety measure which slows down processing, Black will check that the reformatted code still produces a valid AST that is effectively equivalent to the original (see the Pragmatism section for details). If you're feeling confident, use --fast.

The Black code style

Black is a PEP 8 compliant opinionated formatter. Black reformats entire files in place. Style configuration options are deliberately limited and rarely added. It doesn't take previous formatting into account (see Pragmatism for exceptions).

Our documentation covers the current Black code style, but planned changes to it are also documented. They're both worth taking a look:

• The Black Code Style: Current style
• The Black Code Style: Future style

Please refer to this document before submitting an issue. What seems like a bug might be intended behaviour.

Pragmatism

Early versions of Black used to be absolutist in some respects. They took after its initial author. This was fine at the time as it made the implementation simpler and there were not many users anyway. Not many edge cases were reported. As a mature tool, Black does make some exceptions to rules it otherwise holds.

• The Black code style: Pragmatism

Please refer to this document before submitting an issue just like with the document above. What seems like a bug might be intended behaviour.

Configuration

Black is able to read project-specific default values for its command line options from a pyproject.toml file. This is especially useful for specifying custom --include and --exclude/--force-exclude/--extend-exclude patterns for your project.

You can find more details in our documentation:

• The basics: Configuration via a file

And if you're looking for more general configuration documentation:

• Usage and Configuration

Pro-tip: If you're asking yourself "Do I need to configure anything?" the answer is "No". Black is all about sensible defaults. Applying those defaults will have your code in compliance with many other Black formatted projects.

Used by

The following notable open-source projects trust Black with enforcing a consistent code style: pytest, tox, Pyramid, Django Channels, Hypothesis, attrs, SQLAlchemy, Poetry, PyPA applications (Warehouse, Bandersnatch, Pipenv, virtualenv), pandas, Pillow, every Datadog Agent Integration, Home Assistant, Zulip.

The following organizations use Black: Facebook, Dropbox, Mozilla, Quora.

Are we missing anyone? Let us know.

Testimonials

Mike Bayer, author of SQLAlchemy:

I can't think of any single tool in my entire programming career that has given me a bigger productivity increase by its introduction. I can now do refactorings in about 1% of the keystrokes that it would have taken me previously when we had no way for code to format itself.

Dusty Phillips, writer:

Black is opinionated so you don't have to be.

Hynek Schlawack, creator of attrs, core developer of Twisted and CPython:

An auto-formatter that doesn't suck is all I want for Xmas!

Carl Meyer, Django core developer:

At least the name is good.

Kenneth Reitz, creator of requests and pipenv:

This vastly improves the formatting of our code. Thanks a ton!

Show your style

Use the badge in your project's README.md:

[![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)

Using the badge in README.rst:

.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
    :target: https://github.com/psf/black

Looks like this:

License

MIT

Contributing

Welcome! Happy to see you willing to make the project better. You can get started by reading this:

• Contributing: The basics

You can also take a look at the rest of the contributing docs or talk with the developers:

• Contributing documentation
• IRC channel on Freenode

Change log

The log has become rather long. It moved to its own file.

See CHANGES.

Authors

The author list is quite long nowadays, so it lives in its own file.

See AUTHORS.md

Code of Conduct

Everyone participating in the Black project, and in particular in the issue tracker, pull requests, and social media activity, is expected to treat other people with respect and more generally to follow the guidelines articulated in the Python Community Code of Conduct.

At the same time, humor is encouraged. In fact, basic familiarity with Monty Python's Flying Circus is expected. We are not savages.

And if you really need to slap somebody, do it with a fish while dancing.

Change Log

21.5b2

Black

• A space is no longer inserted into empty docstrings (#2249)
• Fix handling of .gitignore files containing non-ASCII characters on Windows (#2229)
• Respect .gitignore files in all levels, not only root/.gitignore file (apply .gitignore rules like git does) (#2225)
• Restored compatibility with Click 8.0 on Python 3.6 when LANG=C used (#2227)
• Add extra uvloop install + import support if in python env (#2258)
• Fix --experimental-string-processing crash when matching parens are not found (#2283)
• Make sure to split lines that start with a string operator (#2286)
• Fix regular expression that black uses to identify f-expressions (#2287)

Blackd

• Add a lower bound for the aiohttp-cors dependency. Only 0.4.0 or higher is supported. (#2231)

Packaging

• Release self-contained x86_64 MacOS binaries as part of the GitHub release pipeline (#2198)
• Always build binaries with the latest available Python (#2260)

Documentation

• Add discussion of magic comments to FAQ page (#2272)
• --experimental-string-processing will be enabled by default in the future (#2273)
• Fix typos discovered by codespell (#2228)
• Fix Vim plugin installation instructions. (#2235)
• Add new Frequently Asked Questions page (#2247)
• Fix encoding + symlink issues preventing proper build on Windows (#2262)

21.5b1

Black

• Refactor src/black/__init__.py into many files (#2206)

Documentation

• Replaced all remaining references to the master branch with the main branch. Some additional changes in the source code were also made. (#2210)
• Sigificantly reorganized the documentation to make much more sense. Check them out by heading over to the stable docs on RTD. (#2174)

21.5b0

Black

• Set --pyi mode if --stdin-filename ends in .pyi (#2169)
• Stop detecting target version as Python 3.9+ with pre-PEP-614 decorators that are being called but with no arguments (#2182)

Black-Primer

• Add --no-diff to black-primer to suppress formatting changes (#2187)

21.4b2

Black

• Fix crash if the user configuration directory is inaccessible. (#2158)

• Clarify circumstances in which Black may change the AST (#2159)

• Allow .gitignore rules to be overridden by specifying exclude in pyproject.toml or on the command line. (#2170)

Packaging

• Install primer.json (used by black-primer by default) with black. (#2154)

21.4b1

Black

• Fix crash on docstrings ending with "\ ". (#2142)

• Fix crash when atypical whitespace is cleaned out of dostrings (#2120)

• Reflect the --skip-magic-trailing-comma and --experimental-string-processing flags in the name of the cache file. Without this fix, changes in these flags would not take effect if the cache had already been populated. (#2131)

• Don't remove necessary parentheses from assignment expression containing assert / return statements. (#2143)

Packaging

• Bump pathspec to >= 0.8.1 to solve invalid .gitignore exclusion handling

21.4b0

Black

• Fixed a rare but annoying formatting instability created by the combination of optional trailing commas inserted by Black and optional parentheses looking at pre-existing "magic" trailing commas. This fixes issue #1629 and all of its many many duplicates. (#2126)

• Black now processes one-line docstrings by stripping leading and trailing spaces, and adding a padding space when needed to break up """". (#1740)

• Black now cleans up leading non-breaking spaces in comments (#2092)

• Black now respects --skip-string-normalization when normalizing multiline docstring quotes (#1637)

• Black no longer removes all empty lines between non-function code and decorators when formatting typing stubs. Now Black enforces a single empty line. (#1646)

• Black no longer adds an incorrect space after a parenthesized assignment expression in if/while statements (#1655)

• Added --skip-magic-trailing-comma / -C to avoid using trailing commas as a reason to split lines (#1824)

• fixed a crash when PWD=/ on POSIX (#1631)

• fixed "I/O operation on closed file" when using --diff (#1664)

• Prevent coloured diff output being interleaved with multiple files (#1673)

• Added support for PEP 614 relaxed decorator syntax on python 3.9 (#1711)

• Added parsing support for unparenthesized tuples and yield expressions in annotated assignments (#1835)

• added --extend-exclude argument (PR #2005)

• speed up caching by avoiding pathlib (#1950)

• --diff correctly indicates when a file doesn't end in a newline (#1662)

• Added --stdin-filename argument to allow stdin to respect --force-exclude rules (#1780)

• Lines ending with fmt: skip will now be not formatted (#1800)

• PR #2053: Black no longer relies on typed-ast for Python 3.8 and higher

• PR #2053: Python 2 support is now optional, install with python3 -m pip install black[python2] to maintain support.

• Exclude venv directory by default (#1683)

• Fixed "Black produced code that is not equivalent to the source" when formatting Python 2 docstrings (#2037)

Packaging

• Self-contained native Black binaries are now provided for releases via GitHub Releases (#1743)

20.8b1

Packaging

• explicitly depend on Click 7.1.2 or newer as Black no longer works with versions older than 7.0

20.8b0

Black

• re-implemented support for explicit trailing commas: now it works consistently within any bracket pair, including nested structures (#1288 and duplicates)

• Black now reindents docstrings when reindenting code around it (#1053)

• Black now shows colored diffs (#1266)

• Black is now packaged using 'py3' tagged wheels (#1388)

• Black now supports Python 3.8 code, e.g. star expressions in return statements (#1121)

• Black no longer normalizes capital R-string prefixes as those have a community-accepted meaning (#1244)

• Black now uses exit code 2 when specified configuration file doesn't exit (#1361)

• Black now works on AWS Lambda (#1141)

• added --force-exclude argument (#1032)

• removed deprecated --py36 option (#1236)

• fixed --diff output when EOF is encountered (#526)

• fixed # fmt: off handling around decorators (#560)

• fixed unstable formatting with some # type: ignore comments (#1113)

• fixed invalid removal on organizing brackets followed by indexing (#1575)

• introduced black-primer, a CI tool that allows us to run regression tests against existing open source users of Black (#1402)

• introduced property-based fuzzing to our test suite based on Hypothesis and Hypothersmith (#1566)

• implemented experimental and disabled by default long string rewrapping (#1132), hidden under a --experimental-string-processing flag while it's being worked on; this is an undocumented and unsupported feature, you lose Internet points for depending on it (#1609)

Vim plugin

• prefer virtualenv packages over global packages (#1383)

19.10b0

• added support for PEP 572 assignment expressions (#711)

• added support for PEP 570 positional-only arguments (#943)

• added support for async generators (#593)

• added support for pre-splitting collections by putting an explicit trailing comma inside (#826)

• added black -c as a way to format code passed from the command line (#761)

• --safe now works with Python 2 code (#840)

• fixed grammar selection for Python 2-specific code (#765)

• fixed feature detection for trailing commas in function definitions and call sites (#763)

• # fmt: off/# fmt: on comment pairs placed multiple times within the same block of code now behave correctly (#1005)

• Black no longer crashes on Windows machines with more than 61 cores (#838)

• Black no longer crashes on standalone comments prepended with a backslash (#767)

• Black no longer crashes on from ... import blocks with comments (#829)

• Black no longer crashes on Python 3.7 on some platform configurations (#494)

• Black no longer fails on comments in from-imports (#671)

• Black no longer fails when the file starts with a backslash (#922)

• Black no longer merges regular comments with type comments (#1027)

• Black no longer splits long lines that contain type comments (#997)

• removed unnecessary parentheses around yield expressions (#834)

• added parentheses around long tuples in unpacking assignments (#832)

• added parentheses around complex powers when they are prefixed by a unary operator (#646)

• fixed bug that led Black format some code with a line length target of 1 (#762)

• Black no longer introduces quotes in f-string subexpressions on string boundaries (#863)

• if Black puts parenthesis around a single expression, it moves comments to the wrapped expression instead of after the brackets (#872)

• blackd now returns the version of Black in the response headers (#1013)

• blackd can now output the diff of formats on source code when the X-Diff header is provided (#969)

19.3b0

• new option --target-version to control which Python versions Black-formatted code should target (#618)

• deprecated --py36 (use --target-version=py36 instead) (#724)

• Black no longer normalizes numeric literals to include _ separators (#696)

• long del statements are now split into multiple lines (#698)

• type comments are no longer mangled in function signatures

• improved performance of formatting deeply nested data structures (#509)

• Black now properly formats multiple files in parallel on Windows (#632)

• Black now creates cache files atomically which allows it to be used in parallel pipelines (like xargs -P8) (#673)

• Black now correctly indents comments in files that were previously formatted with tabs (#262)

• blackd now supports CORS (#622)

18.9b0

• numeric literals are now formatted by Black (#452, #461, #464, #469):

  • numeric literals are normalized to include _ separators on Python 3.6+ code

  • added --skip-numeric-underscore-normalization to disable the above behavior and leave numeric underscores as they were in the input

  • code with _ in numeric literals is recognized as Python 3.6+

  • most letters in numeric literals are lowercased (e.g., in 1e10, 0x01)

  • hexadecimal digits are always uppercased (e.g. 0xBADC0DE)

• added blackd, see its documentation for more info (#349)

• adjacent string literals are now correctly split into multiple lines (#463)

• trailing comma is now added to single imports that don't fit on a line (#250)

• cache is now populated when --check is successful for a file which speeds up consecutive checks of properly formatted unmodified files (#448)

• whitespace at the beginning of the file is now removed (#399)

• fixed mangling pweave and Spyder IDE special comments (#532)

• fixed unstable formatting when unpacking big tuples (#267)

• fixed parsing of __future__ imports with renames (#389)

• fixed scope of # fmt: off when directly preceding yield and other nodes (#385)

• fixed formatting of lambda expressions with default arguments (#468)

• fixed async for statements: Black no longer breaks them into separate lines (#372)

• note: the Vim plugin stopped registering ,= as a default chord as it turned out to be a bad idea (#415)

18.6b4

• hotfix: don't freeze when multiple comments directly precede # fmt: off (#371)

18.6b3

• typing stub files (.pyi) now have blank lines added after constants (#340)

• # fmt: off and # fmt: on are now much more dependable:

  • they now work also within bracket pairs (#329)

  • they now correctly work across function/class boundaries (#335)

  • they now work when an indentation block starts with empty lines or misaligned comments (#334)

• made Click not fail on invalid environments; note that Click is right but the likelihood we'll need to access non-ASCII file paths when dealing with Python source code is low (#277)

• fixed improper formatting of f-strings with quotes inside interpolated expressions (#322)

• fixed unnecessary slowdown when long list literals where found in a file

• fixed unnecessary slowdown on AST nodes with very many siblings

• fixed cannibalizing backslashes during string normalization

• fixed a crash due to symbolic links pointing outside of the project directory (#338)

18.6b2

• added --config (#65)

• added -h equivalent to --help (#316)

• fixed improper unmodified file caching when -S was used

• fixed extra space in string unpacking (#305)

• fixed formatting of empty triple quoted strings (#313)

• fixed unnecessary slowdown in comment placement calculation on lines without comments

18.6b1

• hotfix: don't output human-facing information on stdout (#299)

• hotfix: don't output cake emoji on non-zero return code (#300)

18.6b0

• added --include and --exclude (#270)

• added --skip-string-normalization (#118)

• added --verbose (#283)

• the header output in --diff now actually conforms to the unified diff spec

• fixed long trivial assignments being wrapped in unnecessary parentheses (#273)

• fixed unnecessary parentheses when a line contained multiline strings (#232)

• fixed stdin handling not working correctly if an old version of Click was used (#276)

• Black now preserves line endings when formatting a file in place (#258)

18.5b1

• added --pyi (#249)

• added --py36 (#249)

• Python grammar pickle caches are stored with the formatting caches, making Black work in environments where site-packages is not user-writable (#192)

• Black now enforces a PEP 257 empty line after a class-level docstring (and/or fields) and the first method

• fixed invalid code produced when standalone comments were present in a trailer that was omitted from line splitting on a large expression (#237)

• fixed optional parentheses being removed within # fmt: off sections (#224)

• fixed invalid code produced when stars in very long imports were incorrectly wrapped in optional parentheses (#234)

• fixed unstable formatting when inline comments were moved around in a trailer that was omitted from line splitting on a large expression (#238)

• fixed extra empty line between a class declaration and the first method if no class docstring or fields are present (#219)

• fixed extra empty line between a function signature and an inner function or inner class (#196)

18.5b0

• call chains are now formatted according to the fluent interfaces style (#67)

• data structure literals (tuples, lists, dictionaries, and sets) are now also always exploded like imports when they don't fit in a single line (#152)

• slices are now formatted according to PEP 8 (#178)

• parentheses are now also managed automatically on the right-hand side of assignments and return statements (#140)

• math operators now use their respective priorities for delimiting multiline expressions (#148)

• optional parentheses are now omitted on expressions that start or end with a bracket and only contain a single operator (#177)

• empty parentheses in a class definition are now removed (#145, #180)

• string prefixes are now standardized to lowercase and u is removed on Python 3.6+ only code and Python 2.7+ code with the unicode_literals future import (#188, #198, #199)

• typing stub files (.pyi) are now formatted in a style that is consistent with PEP 484 (#207, #210)

• progress when reformatting many files is now reported incrementally

• fixed trailers (content with brackets) being unnecessarily exploded into their own lines after a dedented closing bracket (#119)

• fixed an invalid trailing comma sometimes left in imports (#185)

• fixed non-deterministic formatting when multiple pairs of removable parentheses were used (#183)

• fixed multiline strings being unnecessarily wrapped in optional parentheses in long assignments (#215)

• fixed not splitting long from-imports with only a single name

• fixed Python 3.6+ file discovery by also looking at function calls with unpacking. This fixed non-deterministic formatting if trailing commas where used both in function signatures with stars and function calls with stars but the former would be reformatted to a single line.

• fixed crash on dealing with optional parentheses (#193)

• fixed "is", "is not", "in", and "not in" not considered operators for splitting purposes

• fixed crash when dead symlinks where encountered

18.4a4

• don't populate the cache on --check (#175)

18.4a3

• added a "cache"; files already reformatted that haven't changed on disk won't be reformatted again (#109)

• --check and --diff are no longer mutually exclusive (#149)

• generalized star expression handling, including double stars; this fixes multiplication making expressions "unsafe" for trailing commas (#132)

• Black no longer enforces putting empty lines behind control flow statements (#90)

• Black now splits imports like "Mode 3 + trailing comma" of isort (#127)

• fixed comment indentation when a standalone comment closes a block (#16, #32)

• fixed standalone comments receiving extra empty lines if immediately preceding a class, def, or decorator (#56, #154)

• fixed --diff not showing entire path (#130)

• fixed parsing of complex expressions after star and double stars in function calls (#2)

• fixed invalid splitting on comma in lambda arguments (#133)

• fixed missing splits of ternary expressions (#141)

18.4a2

• fixed parsing of unaligned standalone comments (#99, #112)

• fixed placement of dictionary unpacking inside dictionary literals (#111)

• Vim plugin now works on Windows, too

• fixed unstable formatting when encountering unnecessarily escaped quotes in a string (#120)

18.4a1

• added --quiet (#78)

• added automatic parentheses management (#4)

• added pre-commit integration (#103, #104)

• fixed reporting on --check with multiple files (#101, #102)

• fixed removing backslash escapes from raw strings (#100, #105)

18.4a0

• added --diff (#87)

• add line breaks before all delimiters, except in cases like commas, to better comply with PEP 8 (#73)

• standardize string literals to use double quotes (almost) everywhere (#75)

• fixed handling of standalone comments within nested bracketed expressions; Black will no longer produce super long lines or put all standalone comments at the end of the expression (#22)

• fixed 18.3a4 regression: don't crash and burn on empty lines with trailing whitespace (#80)

• fixed 18.3a4 regression: # yapf: disable usage as trailing comment would cause Black to not emit the rest of the file (#95)

• when CTRL+C is pressed while formatting many files, Black no longer freaks out with a flurry of asyncio-related exceptions

• only allow up to two empty lines on module level and only single empty lines within functions (#74)

18.3a4

• # fmt: off and # fmt: on are implemented (#5)

• automatic detection of deprecated Python 2 forms of print statements and exec statements in the formatted file (#49)

• use proper spaces for complex expressions in default values of typed function arguments (#60)

• only return exit code 1 when --check is used (#50)

• don't remove single trailing commas from square bracket indexing (#59)

• don't omit whitespace if the previous factor leaf wasn't a math operator (#55)

• omit extra space in kwarg unpacking if it's the first argument (#46)

• omit extra space in Sphinx auto-attribute comments (#68)

18.3a3

• don't remove single empty lines outside of bracketed expressions (#19)

• added ability to pipe formatting from stdin to stdin (#25)

• restored ability to format code with legacy usage of async as a name (#20, #42)

• even better handling of numpy-style array indexing (#33, again)

18.3a2

• changed positioning of binary operators to occur at beginning of lines instead of at the end, following a recent change to PEP 8 (#21)

• ignore empty bracket pairs while splitting. This avoids very weirdly looking formattings (#34, #35)

• remove a trailing comma if there is a single argument to a call

• if top level functions were separated by a comment, don't put four empty lines after the upper function

• fixed unstable formatting of newlines with imports

• fixed unintentional folding of post scriptum standalone comments into last statement if it was a simple statement (#18, #28)

• fixed missing space in numpy-style array indexing (#33)

• fixed spurious space after star-based unary expressions (#31)

18.3a1

• added --check

• only put trailing commas in function signatures and calls if it's safe to do so. If the file is Python 3.6+ it's always safe, otherwise only safe if there are no *args or **kwargs used in the signature or call. (#8)

• fixed invalid spacing of dots in relative imports (#6, #13)

• fixed invalid splitting after comma on unpacked variables in for-loops (#23)

• fixed spurious space in parenthesized set expressions (#7)

• fixed spurious space after opening parentheses and in default arguments (#14, #17)

• fixed spurious space after unary operators when the operand was a complex expression (#15)

18.3a0

• first published version, Happy 🍰 Day 2018!

• alpha quality

• date-versioned (see: https://calver.org/)