Package: blacker
The Uncompromising Code Formatter“Any color you like.”Blackis the uncompromising Python code formatter. By using it, you agree to cede
control over minutiae of hand-formatting. In return,Blackgives you speed,
determinism, and freedom frompycodestylenagging 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.Blackmakes code review faster by producing the smallest diffs possible.Try it out now using theBlack Playground. Watch thePyCon 2019 talkto learn more.Contents:Installation and usage|Code style|pyproject.toml|Editor integration|blackd|Version control integration|Ignoring unmodified files|Used by|Testimonials|Show your style|Contributing|Change Log|AuthorsInstallation and usageInstallationBlackcan be installed by runningpip install black. It requires Python 3.6.0+ to
run but you can reformat Python 2 code with it, too.UsageTo get started right away with sensible defaults:black {source_file_or_directory}Command line optionsBlackdoesn't provide many options. You can list them by runningblack --help:black [OPTIONS] [SRC]...

Options:
  -c, --code TEXT                 Format the code passed in as a string.
  -l, --line-length INTEGER       How many characters per line to allow.
                                  [default: 88]
  -t, --target-version [py27|py33|py34|py35|py36|py37|py38]
                                  Python versions that should be supported by
                                  Black's output. [default: per-file auto-
                                  detection]
  --py36                          Allow using Python 3.6-only syntax on all
                                  input files.  This will put trailing commas
                                  in function signatures and calls also after
                                  *args and **kwargs. Deprecated; use
                                  --target-version instead. [default: per-file
                                  auto-detection]
  --pyi                           Format all input files like typing stubs
                                  regardless of file extension (useful when
                                  piping source on standard input).
  -S, --skip-string-normalization
                                  Don't normalize string quotes or prefixes.
  --check                         Don't write the files back, just return the
                                  status.  Return code 0 means nothing would
                                  change.  Return code 1 means some files
                                  would be reformatted.  Return code 123 means
                                  there was an internal error.
  --diff                          Don't write the files back, just output a
                                  diff for each file on stdout.
  --fast / --safe                 If --fast given, skip temporary sanity
                                  checks. [default: --safe]
  --include TEXT                  A regular expression that matches files and
                                  directories that should be included on
                                  recursive searches.  An empty value means
                                  all files are included regardless of the
                                  name.  Use forward slashes for directories
                                  on all platforms (Windows, too).  Exclusions
                                  are calculated first, inclusions later.
                                  [default: \.pyi?$]
  --exclude TEXT                  A regular expression that matches files and
                                  directories that should be excluded on
                                  recursive searches.  An empty value means no
                                  paths are excluded. Use forward slashes for
                                  directories on all platforms (Windows, too).
                                  Exclusions are calculated first, inclusions
                                  later.  [default: /(\.eggs|\.git|\.hg|\.mypy
                                  _cache|\.nox|\.tox|\.venv|_build|buck-
                                  out|build|dist)/]
  -q, --quiet                     Don't emit non-error messages to stderr.
                                  Errors are still emitted, silence those with
                                  2>/dev/null.
  -v, --verbose                   Also emit messages to stderr about files
                                  that were not changed or were ignored due to
                                  --exclude=.
  --version                       Show the version and exit.
  --config PATH                   Read configuration from PATH.
  -h, --help                      Show this message and exit.Blackis a well-behaved Unix-style command-line tool:it does nothing if no sources are passed to it;it will read from standard input and write to standard output if-is used as the
filename;it only outputs messages to users on standard error;exits with code 0 unless an internal error occurred (or--checkwas used).NOTE: This is a beta productBlackis alreadysuccessfully usedby many projects, small and big. It
also sports a decent test suite. However, it is still very new. 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 thatuntil 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 temporary safety measure,Blackwill check that the reformatted code still
produces a valid AST that is equivalent to the original. This slows it down. If you're
feeling confident, use--fast.TheBlackcode styleBlackreformats entire files in place. It is not configurable. It doesn't take
previous formatting into account. It doesn't reformat blocks that start with# fmt: offand end with# fmt: on.# fmt: on/offhave to be on the same level of
indentation. It also recognizesYAPF's block comments
to the same effect, as a courtesy for straddling code.HowBlackwraps linesBlackignores previous formatting and applies uniform horizontal and vertical
whitespace to your code. The rules for horizontal whitespace can be summarized as: do
whatever makespycodestylehappy. The coding style used byBlackcan be viewed as a
strict subset of PEP 8.As for vertical whitespace,Blacktries to render one full expression or simple
statement per line. If this fits the allotted line length, great.# in:j=[1,2,3]# out:j=[1,2,3]If not,Blackwill look at the contents of the first outer matching brackets and put
that in a separate indented line.# in:ImportantClass.important_method(exc,limit,lookup_lines,capture_locals,extra_argument)# out:ImportantClass.important_method(exc,limit,lookup_lines,capture_locals,extra_argument)If that still doesn't fit the bill, it will decompose the internal expression further
using the same rule, indenting matching brackets every time. If the contents of the
matching brackets pair are comma-separated (like an argument list, or a dict literal,
and so on) thenBlackwill first try to keep them on the same line with the matching
brackets. If that doesn't work, it will put all of them in separate lines.# in:defvery_important_function(template:str,*variables,file:os.PathLike,engine:str,header:bool=True,debug:bool=False):"""Applies `variables` to the `template` and writes to `file`."""withopen(file,'w')asf:...# out:defvery_important_function(template:str,*variables,file:os.PathLike,engine:str,header:bool=True,debug:bool=False,):"""Applies `variables` to the `template` and writes to `file`."""withopen(file,"w")asf:...You might have noticed that closing brackets are always dedented and that a trailing
comma is always added. Such formatting produces smaller diffs; when you add or remove an
element, it's always just one line. Also, having the closing bracket dedented provides a
clear delimiter between two distinct sections of the code that otherwise share the same
indentation level (like the arguments list and the docstring in the example above).If a data structure literal (tuple, list, set, dict) or a line of "from" imports cannot
fit in the allotted length, it's always split into one element per line. This minimizes
diffs as well as enables readers of code to find which commit introduced a particular
entry. This also makesBlackcompatible withisortwith
the following configuration.A compatible `.isort.cfg`[settings]
multi_line_output=3
include_trailing_comma=True
force_grid_wrap=0
use_parentheses=True
line_length=88The equivalent command line is:$ isort --multi-line=3 --trailing-comma --force-grid-wrap=0 --use-parentheses --line-width=88 [ file.py ]Line lengthYou probably noticed the peculiar default line length.Blackdefaults to 88 characters
per line, which happens to be 10% over 80. This number was found to produce
significantly shorter files than sticking with 80 (the most popular), or even 79 (used
by the standard library). In general,90-ish seems like the wise choice.If you're paid by the line of code you write, you can pass--line-lengthwith a lower
number.Blackwill try to respect that. However, sometimes it won't be able to without
breaking other rules. In those rare cases, auto-formatted code will exceed your allotted
limit.You can also increase it, but remember that people with sight disabilities find it
harder to work with line lengths exceeding 100 characters. It also adversely affects
side-by-side diff review on typical screen resolutions. Long lines also make it harder
to present code neatly in documentation or talk slides.If you're using Flake8, you can bumpmax-line-lengthto 88 and forget about it.
Alternatively, useBugbear's B950 warning
instead of E501 and keep the max line length at 80 which you are probably already using.
You'd do it like this:[flake8]max-line-length=80...select=C,E,F,W,B,B950ignore=E203, E501, W503You'll findBlack's own .flake8 config file is configured like this. Explanation of
why W503 and E203 are disabled can be found further in this documentation. And if you're
curious about the reasoning behind B950,Bugbear's documentationexplains it. The tl;dr is "it's like highway speed limits, we won't bother you if you
overdo it by a few km/h".If you're looking for a minimal, black-compatible flake8 configuration:[flake8]max-line-length=88extend-ignore=E203Empty linesBlackavoids spurious vertical whitespace. This is in the spirit of PEP 8 which says
that in-function vertical whitespace should only be used sparingly.Blackwill allow single empty lines inside functions, and single and double empty
lines on module level left by the original editors, except when they're within
parenthesized expressions. Since such expressions are always reformatted to fit minimal
space, this whitespace is lost.It will also insert proper spacing before and after function definitions. It's one line
before and after inner functions and two lines before and after module-level functions
and classes.Blackwill not put empty lines between function/class definitions and
standalone comments that immediately precede the given function/class.Blackwill enforce single empty lines between a class-level docstring and the first
following field or method. This conforms toPEP 257.Blackwon't insert empty lines after function docstrings unless that empty line is
required due to an inner function starting immediately after.Trailing commasBlackwill add trailing commas to expressions that are split by comma where each
element is on its own line. This includes function signatures.Unnecessary trailing commas are removed if an expression fits in one line. This makes it
1% more likely that your line won't exceed the allotted line length limit. Moreover, in
this scenario, if you added another argument to your call, you'd probably fit it in the
same line anyway. That doesn't make diffs any larger.One exception to removing trailing commas is tuple expressions with just one element. In
this caseBlackwon't touch the single trailing comma as this would unexpectedly
change the underlying data type. Note that this is also the case when commas are used
while indexing. This is a tuple in disguise:numpy_array[3, ].One exception to adding trailing commas is function signatures containing*,*args,
or**kwargs. In this case a trailing comma is only safe to use on Python 3.6.Blackwill detect if your file is already 3.6+ only and use trailing commas in this situation.
If you wonder how it knows, it looks for f-strings and existing use of trailing commas
in function signatures that have stars in them. In other words, if you'd like a trailing
comma in this situation andBlackdidn't recognize it was safe to do so, put it there
manually andBlackwill keep it.StringsBlackprefers double quotes ("and""") over single quotes ('and'''). It
will replace the latter with the former as long as it does not result in more backslash
escapes than before.Blackalso standardizes string prefixes, making them always lowercase. On top of that,
if your code is already Python 3.6+ only or it's using theunicode_literalsfuture
import,Blackwill removeufrom the string prefix as it is meaningless in those
scenarios.The main reason to standardize on a single form of quotes is aesthetics. Having one kind
of quotes everywhere reduces reader distraction. It will also enable a future version ofBlackto merge consecutive string literals that ended up on the same line (see#26for details).Why settle on double quotes? They anticipate apostrophes in English text. They match the
docstring standard described inPEP 257. An empty
string in double quotes ("") is impossible to confuse with a one double-quote
regardless of fonts and syntax highlighting used. On top of this, double quotes for
strings are consistent with C which Python interacts a lot with.On certain keyboard layouts like US English, typing single quotes is a bit easier than
double quotes. The latter requires use of the Shift key. My recommendation here is to
keep using whatever is faster to type and letBlackhandle the transformation.If you are adoptingBlackin a large project with pre-existing string conventions
(like the popular"single quotes for data, double quotes for human-readable strings"),
you can pass--skip-string-normalizationon the command line. This is meant as an
adoption helper, avoid using this for new projects.Numeric literalsBlackstandardizes most numeric literals to use lowercase letters for the syntactic
parts and uppercase letters for the digits themselves:0xABinstead of0XABand1e10instead of1E10. Python 2 long literals are styled as2Linstead of2lto
avoid confusion betweenland1.Line breaks & binary operatorsBlackwill break a line before a binary operator when splitting a block of code over
multiple lines. This is so thatBlackis compliant with the recent changes in thePEP 8style guide, which emphasizes that this approach improves readability.This behaviour may raiseW503 line break before binary operatorwarnings in style
guide enforcement tools like Flake8. SinceW503is not PEP 8 compliant, you should
tell Flake8 to ignore these warnings.SlicesPEP 8recommendsto treat:in slices as a binary operator with the lowest priority, and to leave an
equal amount of space on either side, except if a parameter is omitted (e.g.ham[1 + 1 :]). It also states that for extended slices, both:operators have to
have the same amount of spacing, except if a parameter is omitted (ham[1 + 1 ::]).Blackenforces these rules consistently.This behaviour may raiseE203 whitespace before ':'warnings in style guide
enforcement tools like Flake8. SinceE203is not PEP 8 compliant, you should tell
Flake8 to ignore these warnings.ParenthesesSome parentheses are optional in the Python grammar. Any expression can be wrapped in a
pair of parentheses to form an atom. There are a few interesting cases:if (...):while (...):for (...) in (...):assert (...), (...)from X import (...)assignments like:target = (...)target: type = (...)some, *un, packing = (...)augmented += (...)In those cases, parentheses are removed when the entire statement fits in one line, or
if the inner expression doesn't have any delimiters to further split on. If there is
only a single delimiter and the expression starts or ends with a bracket, the
parenthesis can also be successfully omitted since the existing bracket pair will
organize the expression neatly anyway. Otherwise, the parentheses are added.Please note thatBlackdoes not add or remove any additional nested parentheses that
you might want to have for clarity or further code organization. For example those
parentheses are not going to be removed:returnnot(thisorthat)decision=(maybe.this()andvalues>0)or(maybe.that()andvalues<0)Call chainsSome popular APIs, like ORMs, use call chaining. This API style is known as afluent interface.Blackformats
those by treating dots that follow a call or an indexing operation like a very low
priority delimiter. It's easier to show the behavior than to explain it. Look at the
example:defexample(session):result=(session.query(models.Customer.id).filter(models.Customer.account_id==account_id,models.Customer.email==email_address,).order_by(models.Customer.id.asc()).all())Typing stub filesPEP 484 describes the syntax for type hints in Python. One of the use cases for typing
is providing type annotations for modules which cannot contain them directly (they might
be written in C, or they might be third-party, or their implementation may be overly
dynamic, and so on).To solve this,stub files with the.pyifile extensioncan be used to describe typing information for an external module. Those stub files omit
the implementation of classes and functions they describe, instead they only contain the
structure of the file (listing globals, functions, and classes with their members). The
recommended code style for those files is more terse than PEP 8:prefer...on the same line as the class/function signature;avoid vertical whitespace between consecutive module-level functions, names, or
methods and fields within a single class;use a single blank line between top-level class definitions, or none if the classes
are very small.Blackenforces the above rules. There are additional guidelines for formatting.pyifile that are not enforced yet but might be in a future version of the formatter:all function bodies should be empty (contain...instead of the body);do not use docstrings;prefer...overpass;for arguments with a default, use...instead of the actual default;avoid using string literals in type annotations, stub files support forward references
natively (like Python 3.7 code withfrom __future__ import annotations);use variable annotations instead of type comments, even for stubs that target older
versions of Python;for arguments that default toNone, useOptional[]explicitly;usefloatinstead ofUnion[int, float].pyproject.tomlBlackis able to read project-specific default values for its command line options
from apyproject.tomlfile. This is especially useful for specifying custom--includeand--excludepatterns for your project.Pro-tip: If you're asking yourself "Do I need to configure anything?" the answer is
"No".Blackis all about sensible defaults.What on Earth is apyproject.tomlfile?PEP 518definespyproject.tomlas a
configuration file to store build system requirements for Python projects. With the help
of tools likePoetryorFlitit can fully replace the need forsetup.pyandsetup.cfgfiles.WhereBlacklooks for the fileBy defaultBlacklooks forpyproject.tomlstarting from the common base directory of
all files and directories passed on the command line. If it's not there, it looks in
parent directories. It stops looking when it finds the file, or a.gitdirectory, or a.hgdirectory, or the root of the file system, whichever comes first.If you're formatting standard input,Blackwill look for configuration starting from
the current working directory.You can also explicitly specify the path to a particular file that you want with--config. In this situationBlackwill not look for any other file.If you're running with--verbose, you will see a blue message if a file was found and
used.Please noteblackdwill not usepyproject.tomlconfiguration.Configuration formatAs the file extension suggests,pyproject.tomlis aTOMLfile. It contains separate sections for
different tools.Blackis using the[tool.black]section. The option keys are the
same as long names of options on the command line.Note that you have to use single-quoted strings in TOML for regular expressions. It's
the equivalent of r-strings in Python. Multiline strings are treated as verbose regular
expressions by Black. Use[ ]to denote a significant space character.Example `pyproject.toml`[tool.black]line-length=88target-version=['py37']include='\.pyi?$'exclude='''(/(\.eggs         # exclude a few common directories in the| \.git          # root of the project| \.hg| \.mypy_cache| \.tox| \.venv| _build| buck-out| build| dist)/| foo.py           # also separately exclude a file named foo.py in# the root of the project)'''Lookup hierarchyCommand-line options have defaults that you can see in--help. Apyproject.tomlcan
override those defaults. Finally, options provided by the user on the command line
override both.Blackwill only ever use onepyproject.tomlfile during an entire run. It doesn't
look for multiple files, and doesn't compose configuration from different levels of the
file hierarchy.Editor integrationEmacsUseproofit404/blackenorElpy.PyCharm/IntelliJ IDEAInstallblack.$pipinstallblackLocate yourblackinstallation folder.On macOS / Linux / BSD:$whichblack/usr/local/bin/black  # possible locationOn Windows:$whereblack%LocalAppData%\Programs\Python\Python36-32\Scripts\black.exe# possible locationOpen External tools in PyCharm/IntelliJ IDEAOn macOS:PyCharm -> Preferences -> Tools -> External ToolsOn Windows / Linux / BSD:File -> Settings -> Tools -> External ToolsClick the + icon to add a new external tool with the following values:Name: BlackDescription: Black is the uncompromising Python code formatter.Program: <install_location_from_step_2>Arguments:"$FilePath$"Format the currently opened file by selectingTools -> External Tools -> black.Alternatively, you can set a keyboard shortcut by navigating toPreferences or Settings -> Keymap -> External Tools -> External Tools - Black.Optionally, runBlackon every file save:Make sure you have theFile Watcherplugin
installed.Go toPreferences or Settings -> Tools -> File Watchersand click+to add a
new watcher:Name: BlackFile type: PythonScope: Project FilesProgram: <install_location_from_step_2>Arguments:$FilePath$Output paths to refresh:$FilePath$Working directory:$ProjectFileDir$Uncheck "Auto-save edited files to trigger the watcher"Wing IDEWing supports black via the OS Commands tool, as explained in the Wing documentation onpep8 formatting. The detailed procedure is:Installblack.$pipinstallblackMake sure it runs from the command line, e.g.$black--helpIn Wing IDE, activate theOS Commandspanel and define the commandblackto
execute black on the currently selected file:Use the Tools -> OS Commands menu selectionclick on+inOS Commands-> New: Command line..Title: blackCommand Line: black %sI/O Encoding: Use DefaultKey Binding: F1Raise OS Commands when executedAuto-save files before executionLine modeSelect a file in the editor and pressF1, or whatever key binding you selected
in step 3, to reformat the file.VimCommands and shortcuts::Blackto format the entire file (ranges not supported);:BlackUpgradeto upgradeBlackinside the virtualenv;:BlackVersionto get the current version ofBlackinside the virtualenv.Configuration:g:black_fast(defaults to0)g:black_linelength(defaults to88)g:black_skip_string_normalization(defaults to0)g:black_virtualenv(defaults to~/.vim/blackor~/.local/share/nvim/black)To install withvim-plug:Plug 'psf/black'or withVundle:Plugin 'psf/black'or you can copy the plugin fromplugin/black.vim.mkdir -p ~/.vim/pack/python/start/black/plugin
curl https://raw.githubusercontent.com/psf/black/master/plugin/black.vim -o ~/.vim/pack/python/start/black/plugin/black.vimLet me know if this requires any changes to work with Vim 8's builtinpackadd, or
Pathogen, and so on.This pluginrequires Vim 7.0+ built with Python 3.6+ support. It needs Python 3.6 to
be able to runBlackinside the Vim process which is much faster than calling an
external command.On first run, the plugin creates its own virtualenv using the right Python version and
automatically installsBlack. You can upgrade it later by calling:BlackUpgradeand
restarting Vim.If you need to do anything special to make your virtualenv work and installBlack(for
example you want to run a version from master), create a virtualenv manually and pointg:black_virtualenvto it. The plugin will use it.To runBlackon save, add the following line to.vimrcorinit.vim:autocmd BufWritePre *.py execute ':Black'To runBlackon a key press (e.g. F9 below), add this:nnoremap <F9> :Black<CR>How to get Vim with Python 3.6?On Ubuntu 17.10 Vim comes with Python 3.6 by
default. On macOS with Homebrew run:brew install vim --with-python3. When building
Vim from source, use:./configure --enable-python3interp=yes. There's many guides
online how to do this.Visual Studio CodeUse thePython extension(instructions).SublimeText 3Usesublack plugin.Jupyter Notebook MagicUseblackcellmagic.Python Language ServerIf your editor supports theLanguage Server Protocol(Atom,
Sublime Text, Visual Studio Code and many more), you can use thePython Language Serverwith thepyls-blackplugin.Atom/NuclideUsepython-black.KakouneAdd the following hook to your kakrc, then run black with:format.hook global WinSetOption filetype=python %{
    set-option window formatcmd 'black -q  -'
}ThonnyUseThonny-black-code-format.Other editorsOther editors will require external contributions.Patches welcome! ✨ 🍰 ✨Any tool that can pipe code throughBlackusing its stdio mode (justuse-as the file name).
The formatted code will be returned on stdout (unless--checkwas passed).Blackwill still emit messages on stderr but that shouldn't affect your use case.This can be used for example with PyCharm's or IntelliJ'sFile Watchers.blackdblackdis a small HTTP server that exposesBlack's functionality over a simple
protocol. The main benefit of using it is to avoid paying the cost of starting up a newBlackprocess every time you want to blacken a file.Usageblackdis not packaged alongsideBlackby default because it has additional
dependencies. You will need to dopip install black[d]to install it.You can start the server on the default port, binding only to the local interface by
runningblackd. You will see a single line mentioning the server's version, and the
host and port it's listening on.blackdwill then print an access log similar to most
web servers on standard output, merged with any exception traces caused by invalid
formatting requests.blackdprovides even less options thanBlack. You can see them by runningblackd --help:Usage: blackd [OPTIONS]

Options:
  --bind-host TEXT                Address to bind the server to.
  --bind-port INTEGER             Port to listen on
  --version                       Show the version and exit.
  -h, --help                      Show this message and exit.There is no official blackd client tool (yet!). You can test that blackd is working
usingcurl:blackd --bind-port 9090 &  # or let blackd choose a port
curl -s -XPOST "localhost:9090" -d "print('valid')"Protocolblackdonly acceptsPOSTrequests at the/path. The body of the request should
contain the python source code to be formatted, encoded according to thecharsetfield
in theContent-Typerequest header. If nocharsetis specified,blackdassumesUTF-8.There are a few HTTP headers that control how the source is formatted. These correspond
to command line flags forBlack. There is one exception to this:X-Protocol-Versionwhich if present, should have the value1, otherwise the request is rejected withHTTP 501(Not Implemented).The headers controlling how code is formatted are:X-Line-Length: corresponds to the--line-lengthcommand line flag.X-Skip-String-Normalization: corresponds to the--skip-string-normalizationcommand line flag. If present and its value is not the empty string, no string
normalization will be performed.X-Fast-Or-Safe: if set tofast,blackdwill act asBlackdoes when passed the--fastcommand line flag.X-Python-Variant: if set topyi,blackdwill act asBlackdoes when passed the--pyicommand line flag. Otherwise, its value must correspond to a Python version or
a set of comma-separated Python versions, optionally prefixed withpy. For example,
to request code that is compatible with Python 3.5 and 3.6, set the header topy3.5,py3.6.X-Diff: corresponds to the--diffcommand line flag. If present, a diff of the
formats will be output.If any of these headers are set to invalid values,blackdreturns aHTTP 400error
response, mentioning the name of the problematic header in the message body.Apart from the above,blackdcan produce the following response codes:HTTP 204: If the input is already well-formatted. The response body is empty.HTTP 200: If formatting was needed on the input. The response body contains the
blackened Python code, and theContent-Typeheader is set accordingly.HTTP 400: If the input contains a syntax error. Details of the error are returned in
the response body.HTTP 500: If there was any kind of error while trying to format the input. The
response body contains a textual representation of the error.The response headers include aX-Black-Versionheader containing the version ofBlack.Version control integrationUsepre-commit. Once youhave it installed, add this to the.pre-commit-config.yamlin your repository:repos:-repo:https://github.com/psf/blackrev:stablehooks:-id:blacklanguage_version:python3.6Then runpre-commit installand you're ready to go.Avoid usingargsin the hook. Instead, store necessary configuration inpyproject.tomlso that editors and command-line usage of Black all behave consistently
for your project. SeeBlack's ownpyproject.tomlfor an example.If you're already using Python 3.7, switch thelanguage_versionaccordingly. Finally,stableis a tag that is pinned to the latest release on PyPI. If you'd rather run on
master, this is also an option.Ignoring unmodified filesBlackremembers files it has already formatted, unless the--diffflag is used or
code is passed via standard input. This information is stored per-user. The exact
location of the file depends on theBlackversion and the system on whichBlackis
run. The file is non-portable. The standard location on common operating systems is:Windows:C:\\Users\<username>\AppData\Local\black\black\Cache\<version>\cache.<line-length>.<file-mode>.picklemacOS:/Users/<username>/Library/Caches/black/<version>/cache.<line-length>.<file-mode>.pickleLinux:/home/<username>/.cache/black/<version>/cache.<line-length>.<file-mode>.picklefile-modeis an int flag that determines whether the file was formatted as 3.6+ only,
as .pyi, and whether string normalization was omitted.To override the location of these files on macOS or Linux, set the environment variableXDG_CACHE_HOMEto your preferred location. For example, if you want to put the cache
in the directory you're runningBlackfrom, setXDG_CACHE_HOME=.cache.Blackwill
then write the above files to.cache/black/<version>/.Used byThe following notable open-source projects trustBlackwith enforcing a consistent
code style: pytest, tox, Pyramid, Django Channels, Hypothesis, attrs, SQLAlchemy,
Poetry, PyPA applications (Warehouse, Pipenv, virtualenv), pandas, Pillow, every Datadog
Agent Integration, Home Assistant.Are we missing anyone? Let us know.TestimonialsDusty Phillips,writer:Blackis opinionated so you don't have to be.Hynek Schlawack,creator ofattrs, core developer of
Twisted and CPython:An auto-formatter that doesn't suck is all I want for Xmas!Carl Meyer,Djangocore developer:At least the name is good.Kenneth Reitz, creator ofrequestsandpipenv:This vastly improves the formatting of our code. Thanks a ton!Show your styleUse 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/blackLooks like this:LicenseMITContributing toBlackIn terms of inspiration,Blackis about as configurable asgofmt. This is
deliberate.Bug reports and fixes are always welcome! However, before you suggest a new feature or
configuration knob, ask yourself why you want it. If it enables better integration with
some workflow, fixes an inconsistency, speeds things up, and so on - go for it! On the
other hand, if your answer is "because I don't like a particular formatting" then you're
not ready to embraceBlackyet. Such changes are unlikely to get accepted. You can
still try but prepare to be disappointed.More details can be found inCONTRIBUTING.Change Log19.10b0added 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)addedblack -cas 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: oncomment pairs placed multiple times within the same block of
code now behave correctly (#1005)Blackno longer crashes on Windows machines with more than 61 cores (#838)Blackno longer crashes on standalone comments prepended with a backslash (#767)Blackno longer crashes onfrom...importblocks with comments (#829)Blackno longer crashes on Python 3.7 on some platform configurations (#494)Blackno longer fails on comments in from-imports (#671)Blackno longer fails when the file starts with a backslash (#922)Blackno longer merges regular comments with type comments (#1027)Blackno longer splits long lines that contain type comments (#997)removed unnecessary parentheses aroundyieldexpressions (#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 ledBlackformat some code with a line length target of 1 (#762)Blackno longer introduces quotes in f-string subexpressions on string boundaries
(#863)ifBlackputs parenthesis around a single expression, it moves comments to the
wrapped expression instead of after the brackets (#872)blackdnow returns the version ofBlackin the response headers (#1013)blackdcan now output the diff of formats on source code when theX-Diffheader is
provided (#969)19.3b0new option--target-versionto control which Python versionsBlack-formatted code
should target (#618)deprecated--py36(use--target-version=py36instead) (#724)Blackno longer normalizes numeric literals to include_separators (#696)longdelstatements are now split into multiple lines (#698)type comments are no longer mangled in function signaturesimproved performance of formatting deeply nested data structures (#509)Blacknow properly formats multiple files in parallel on Windows (#632)Blacknow creates cache files atomically which allows it to be used in parallel
pipelines (likexargs -P8) (#673)Blacknow correctly indents comments in files that were previously formatted with
tabs (#262)blackdnow supports CORS (#622)18.9b0numeric literals are now formatted byBlack(#452, #461, #464, #469):numeric literals are normalized to include_separators on Python 3.6+ codeadded--skip-numeric-underscore-normalizationto disable the above behavior and
leave numeric underscores as they were in the inputcode with_in numeric literals is recognized as Python 3.6+most letters in numeric literals are lowercased (e.g., in1e10,0x01)hexadecimal digits are always uppercased (e.g.0xBADC0DE)addedblackd, seeits documentationfor 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--checkis 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 manglingpweaveandSpyder IDEspecial comments (#532)fixed unstable formatting when unpacking big tuples (#267)fixed parsing of__future__imports with renames (#389)fixed scope of# fmt: offwhen directly precedingyieldand other nodes (#385)fixed formatting of lambda expressions with default arguments (#468)fixedasync forstatements:Blackno 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)18.6b4hotfix: don't freeze when multiple comments directly precede# fmt: off(#371)18.6b3typing stub files (.pyi) now have blank lines added after constants (#340)# fmt: offand# fmt: onare 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 filefixed unnecessary slowdown on AST nodes with very many siblingsfixed cannibalizing backslashes during string normalizationfixed a crash due to symbolic links pointing outside of the project directory (#338)18.6b2added--config(#65)added-hequivalent to--help(#316)fixed improper unmodified file caching when-Swas usedfixed extra space in string unpacking (#305)fixed formatting of empty triple quoted strings (#313)fixed unnecessary slowdown in comment placement calculation on lines without comments18.6b1hotfix: don't output human-facing information on stdout (#299)hotfix: don't output cake emoji on non-zero return code (#300)18.6b0added--includeand--exclude(#270)added--skip-string-normalization(#118)added--verbose(#283)the header output in--diffnow actually conforms to the unified diff specfixed 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)Blacknow preserves line endings when formatting a file in place (#258)18.5b1added--pyi(#249)added--py36(#249)Python grammar pickle caches are stored with the formatting caches, makingBlackwork in environments where site-packages is not user-writable (#192)Blacknow enforces a PEP 257 empty line after a class-level docstring (and/or
fields) and the first methodfixed 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: offsections (#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)18.5b0call chains are now formatted according to thefluent interfacesstyle (#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 anduis removed on Python 3.6+
only code and Python 2.7+ code with theunicode_literalsfuture 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 incrementallyfixed 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 namefixed 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
purposesfixed crash when dead symlinks where encountered18.4a4don't populate the cache on--check(#175)18.4a3added a "cache"; files already reformatted that haven't changed on disk won't be
reformatted again (#109)--checkand--diffare no longer mutually exclusive (#149)generalized star expression handling, including double stars; this fixes
multiplication making expressions "unsafe" for trailing commas (#132)Blackno longer enforces putting empty lines behind control flow statements (#90)Blacknow 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--diffnot 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)18.4a2fixed parsing of unaligned standalone comments (#99, #112)fixed placement of dictionary unpacking inside dictionary literals (#111)Vim plugin now works on Windows, toofixed unstable formatting when encountering unnecessarily escaped quotes in a string
(#120)18.4a1added--quiet(#78)added automatic parentheses management (#4)addedpre-commitintegration (#103, #104)fixed reporting on--checkwith multiple files (#101, #102)fixed removing backslash escapes from raw strings (#100, #105)18.4a0added--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;Blackwill 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: disableusage as trailing comment would causeBlackto not emit the rest of the file (#95)when CTRL+C is pressed while formatting many files,Blackno longer freaks out with
a flurry of asyncio-related exceptionsonly allow up to two empty lines on module level and only single empty lines within
functions (#74)18.3a4# fmt: offand# fmt: onare 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 inSphinx auto-attribute comments(#68)18.3a3don'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 ofasyncas a name (#20, #42)even better handling of numpy-style array indexing (#33, again)18.3a2changed positioning of binary operators to occur at beginning of lines instead of at
the end, followinga 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 callif top level functions were separated by a comment, don't put four empty lines after
the upper functionfixed unstable formatting of newlines with importsfixed 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)18.3a1added--checkonly 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*argsor**kwargsused 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)18.3a0first published version, Happy 🍰 Day 2018!alpha qualitydate-versioned (see:https://calver.org/)AuthorsGlued together byŁukasz Langa.Maintained withCarol Willing,Carl Meyer,Jelle Zijlstra,Mika Naylor, andZsolt Dollenstein.Multiple contributions by:Abdur-Rahmaan JanhangeerAdam JohnsonAlexander HuynhAndrew ThorpAndreyAndy FreelandAnthony SottileArjaan BuijkArtem MalyshevAsger Hautop DrewsenAugie FacklerAviskar KCBenjamin WoodruffBrandt BucherCharles ReidChristian HeimesChuck WootersDaniel HahlerDaniel M. CapellaDaniele EspostidylanjblackEli TreuherzFlorent ThieryhauntsaninjaHugo van KemenadeIvan KatanićJason FriedjgirardetJoe AntonakakisJon DufresneJonas ObristJosh BodeJuan Luis Cano RodríguezKatie McLaughlinLawrence ChanLinus GrohLuka SterbicMariattaMatt VanEseltineMichael FlaxmanMichael J. SullivanMichael McClimonMiguel GaiowskiMikeMin ho KimMiroslav ShubernetskiyNerasteOfek LevOsaetin DanielPablo GalindoPeter BengtssonpmacostaRishikesh JhaStavros KorokithakisStephen RosenSunil KapilThom LuTom ChristieTzu-ping ChungUtsav ShahvezeliVishwas B SharmaYngve HøisethYurii Karabas