“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.
Contents: Installation and usage | Code style | Pragmatism | pyproject.toml | Editor integration | blackd | black-primer | Version control integration | Ignoring unmodified files | Used by | Testimonials | Show your style | Contributing | Change Log | Authors
Black can be installed by running pip install black
. It requires Python 3.6.0+ to
run but you can reformat Python 2 code with it, too.
To get started right away with sensible defaults:
black {source_file_or_directory}
Black doesn't provide many options. You can list them by running black --help
:
Usage: black [OPTIONS] [SRC]...
The uncompromising code formatter.
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]
--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.
--color / --no-color Show colored diff. Only applies when
`--diff` is given.
--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|\.svn|_build|buck-
out|build|dist)/]
--force-exclude TEXT Like --exclude, but files and directories
matching this regex will be excluded even
when they are passed explicitly as arguments
-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 FILE Read configuration from PATH.
-h, --help Show this message and exit.
Black is 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
--check
was used).
While Black enforces formatting that conforms to PEP 8, other tools may raise warnings about Black's changes or will overwrite Black's changes. A good example of this is isort. Since Black is barely configurable, these tools should be configured to neither warn about nor overwrite Black's changes.
Actual details on Black compatible configurations for various tools can be found in compatible_configs.
A long-standing argument against moving to automated code formatters like Black is
that the migration will clutter up the output of git blame
. This was a valid argument,
but since Git version 2.23, Git natively supports
ignoring revisions in blame
with the --ignore-rev
option. You can also pass a file listing the revisions to ignore
using the --ignore-revs-file
option. The changes made by the revision will be ignored
when assigning blame. Lines modified by an ignored revision will be blamed on the
previous revision that modified those lines.
So when migrating your project's code style to Black, reformat everything and commit the changes (preferably in one massive commit). Then put the full 40 characters commit identifier(s) into a file.
# Migrate code style to Black
5b4ab991dede475d393e9d69ec388fd6bd949699
Afterwards, you can pass that file to git blame
and see clean and meaningful blame
information.
$ git blame important.py --ignore-revs-file .git-blame-ignore-revs
7a1ae265 (John Smith 2019-04-15 15:55:13 -0400 1) def very_important_function(text, file):
abdfd8b0 (Alice Doe 2019-09-23 11:39:32 -0400 2) text = text.lstrip()
7a1ae265 (John Smith 2019-04-15 15:55:13 -0400 3) with open(file, "r+") as f:
7a1ae265 (John Smith 2019-04-15 15:55:13 -0400 4) f.write(formatted)
You can even configure git
to automatically ignore revisions listed in a file on every
call to git blame
.
$ git config blame.ignoreRevsFile .git-blame-ignore-revs
The one caveat is that GitHub and GitLab do not yet support ignoring revisions using their native UI of blame. So blame information will be cluttered with a reformatting commit on those platforms. (If you'd like this feature, there's an open issue for GitLab and please let GitHub know!)
Black is already successfully used by 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 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 temporary safety measure, Black will 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
.
Black reformats 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: off
and end with # fmt: on
. # fmt: on/off
have to be on the same level of
indentation. It also recognizes YAPF's block comments
to the same effect, as a courtesy for straddling code.
Black ignores previous formatting and applies uniform horizontal and vertical
whitespace to your code. The rules for horizontal whitespace can be summarized as: do
whatever makes pycodestyle
happy. The coding style used by Black can be viewed as a
strict subset of PEP 8.
As for vertical whitespace, Black tries 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, Black will 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) then Black will 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:
def very_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`."""
with open(file, 'w') as f:
...
# out:
def very_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`."""
with open(file, "w") as f:
...
Black prefers parentheses over backslashes, and will remove backslashes if found.
# in:
if some_short_rule1 \
and some_short_rule2:
...
# out:
if some_short_rule1 and some_short_rule2:
...
# in:
if some_long_rule1 \
and some_long_rule2:
...
# out:
if (
some_long_rule1
and some_long_rule2
):
...
Backslashes and multiline strings are one of the two places in the Python grammar that break significant indentation. You never need backslashes, they are used to force the grammar to accept breaks that would otherwise be parse errors. That makes them confusing to look at and brittle to modify. This is why Black always gets rid of them.
If you're reaching for backslashes, that's a clear signal that you can do better if you slightly refactor your code. I hope some of the examples above show you that there are many ways in which you can do it.
However there is one exception: with
statements using multiple context managers.
Python's grammar does not allow organizing parentheses around the series of context
managers.
We don't want formatting like:
with make_context_manager1() as cm1, make_context_manager2() as cm2, make_context_manager3() as cm3, make_context_manager4() as cm4:
... # nothing to split on - line too long
So Black will now format it like this:
with \
make_context_manager(1) as cm1, \
make_context_manager(2) as cm2, \
make_context_manager(3) as cm3, \
make_context_manager(4) as cm4 \
:
... # backslashes and an ugly stranded colon
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 makes Black compatible with isort with 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=88
The equivalent command line is:
$ isort --multi-line=3 --trailing-comma --force-grid-wrap=0 --use-parentheses --line-width=88 [ file.py ]
You probably noticed the peculiar default line length. Black defaults 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-length
with a lower
number. Black will 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 bump max-line-length
to 88 and forget about it.
Alternatively, use Bugbear'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,B950
ignore = E203, E501, W503
You'll find Black'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 documentation explains 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 = 88
extend-ignore = E203
Black avoids spurious vertical whitespace. This is in the spirit of PEP 8 which says that in-function vertical whitespace should only be used sparingly.
Black will 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. Black will not put empty lines between function/class definitions and standalone comments that immediately precede the given function/class.
Black will enforce single empty lines between a class-level docstring and the first following field or method. This conforms to PEP 257.
Black won't insert empty lines after function docstrings unless that empty line is required due to an inner function starting immediately after.
Black will 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 case Black won'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. Black
will 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 and Black didn't recognize it was safe to do so, put it there
manually and Black will keep it.
Black prefers 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.
Black also standardizes string prefixes, making them always lowercase. On top of that,
if your code is already Python 3.6+ only or it's using the unicode_literals
future
import, Black will remove u
from 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 of Black to merge consecutive string literals that ended up on the same line (see #26 for details).
Why settle on double quotes? They anticipate apostrophes in English text. They match the
docstring standard described in
PEP 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 let Black handle the transformation.
If you are adopting Black in 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-normalization
on the command line. This is meant as an
adoption helper, avoid using this for new projects.
Black standardizes most numeric literals to use lowercase letters for the syntactic
parts and uppercase letters for the digits themselves: 0xAB
instead of 0XAB
and
1e10
instead of 1E10
. Python 2 long literals are styled as 2L
instead of 2l
to
avoid confusion between l
and 1
.
Black will break a line before a binary operator when splitting a block of code over multiple lines. This is so that Black is compliant with the recent changes in the PEP 8 style guide, which emphasizes that this approach improves readability.
This behaviour may raise W503 line break before binary operator
warnings in style
guide enforcement tools like Flake8. Since W503
is not PEP 8 compliant, you should
tell Flake8 to ignore these warnings.
PEP 8
recommends
to 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 recommends no spaces around :
operators for "simple expressions"
(ham[lower:upper]
), and extra space for "complex expressions"
(ham[lower : upper + offset]
). Black treats anything more than variable names as
"complex" (ham[lower : upper + 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 ::]
). Black enforces these rules consistently.
This behaviour may raise E203 whitespace before ':'
warnings in style guide
enforcement tools like Flake8. Since E203
is not PEP 8 compliant, you should tell
Flake8 to ignore these warnings.
Some 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 that Black does 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:
return not (this or that)
decision = (maybe.this() and values > 0) or (maybe.that() and values < 0)
Some popular APIs, like ORMs, use call chaining. This API style is known as a fluent interface. Black formats 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:
def example(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()
)
PEP 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 .pyi
file extension
can 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.
Black enforces the above rules. There are additional guidelines for formatting .pyi
file 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 with
from __future__ import annotations
); - use variable annotations instead of type comments, even for stubs that target older versions of Python;
- for arguments that default to
None
, useOptional[]
explicitly; - use
float
instead ofUnion[int, float]
.
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. This section documents what those exceptions are and why this is the case.
Black in general does not take existing formatting into account.
However, there are cases where you put a short collection or function call in your code but you anticipate it will grow in the future.
For example:
TRANSLATIONS = {
"en_us": "English (US)",
"pl_pl": "polski",
}
Early versions of Black used to ruthlessly collapse those into one line (it fits!). Now, you can communicate that you don't want that by putting a trailing comma in the collection yourself. When you do, Black will know to always explode your collection into one item per line.
How do you make it stop? Just delete that trailing comma and Black will collapse your collection into one line if it fits.
Black normalizes string quotes as well as string prefixes, making them lowercase. One exception to this rule is r-strings. It turns out that the very popular MagicPython syntax highlighter, used by default by (among others) GitHub and Visual Studio Code, differentiates between r-strings and R-strings. The former are syntax highlighted as regular expressions while the latter are treated as true raw strings with no special semantics.
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
patterns for your project.
Pro-tip: If you're asking yourself "Do I need to configure anything?" the answer is "No". Black is all about sensible defaults.
PEP 518 defines pyproject.toml
as a
configuration file to store build system requirements for Python projects. With the help
of tools like Poetry or
Flit it can fully replace the need for
setup.py
and setup.cfg
files.
By default Black looks for pyproject.toml
starting 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 .git
directory, or a
.hg
directory, or the root of the file system, whichever comes first.
If you're formatting standard input, Black will 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 situation Black will 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 note blackd
will not use pyproject.toml
configuration.
As the file extension suggests, pyproject.toml
is a
TOML file. It contains separate sections for
different tools. Black is 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 = 88
target-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
)
'''
Command-line options have defaults that you can see in --help
. A pyproject.toml
can
override those defaults. Finally, options provided by the user on the command line
override both.
Black will only ever use one pyproject.toml
file during an entire run. It doesn't
look for multiple files, and doesn't compose configuration from different levels of the
file hierarchy.
Options include the following:
- Install
black
.
$ pip install black
- Locate your
black
installation folder.
On macOS / Linux / BSD:
$ which black
/usr/local/bin/black # possible location
On Windows:
$ where black
%LocalAppData%\Programs\Python\Python36-32\Scripts\black.exe # possible location
Note that if you are using a virtual environment detected by PyCharm, this is an
unneeded step. In this case the path to black
is $PyInterpreterDirectory$/black
.
- Open External tools in PyCharm/IntelliJ IDEA
On macOS:
PyCharm -> Preferences -> Tools -> External Tools
On Windows / Linux / BSD:
File -> Settings -> Tools -> External Tools
-
Click the + icon to add a new external tool with the following values:
- Name: Black
- Description: Black is the uncompromising Python code formatter.
- Program: <install_location_from_step_2>
- Arguments:
"$FilePath$"
-
Format the currently opened file by selecting
Tools -> External Tools -> black
.- Alternatively, you can set a keyboard shortcut by navigating to
Preferences or Settings -> Keymap -> External Tools -> External Tools - Black
.
- Alternatively, you can set a keyboard shortcut by navigating to
-
Optionally, run Black on every file save:
- Make sure you have the File Watcher plugin installed.
- Go to
Preferences or Settings -> Tools -> File Watchers
and click+
to add a new watcher:- Name: Black
- File type: Python
- Scope: Project Files
- Program: <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 supports black via the OS Commands tool, as explained in the Wing documentation on pep8 formatting. The detailed procedure is:
- Install
black
.
$ pip install black
- Make sure it runs from the command line, e.g.
$ black --help
- In Wing IDE, activate the OS Commands panel and define the command black to execute black on the currently selected file:
- Use the Tools -> OS Commands menu selection
- click on + in OS Commands -> New: Command line..
- Title: black
- Command Line: black %s
- I/O Encoding: Use Default
- Key Binding: F1
- Raise OS Commands when executed
- Auto-save files before execution
- Line mode
- Select a file in the editor and press F1 , or whatever key binding you selected in step 3, to reformat the file.
Commands and shortcuts:
:Black
to format the entire file (ranges not supported);:BlackUpgrade
to upgrade Black inside the virtualenv;:BlackVersion
to get the current version of Black inside 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/black
or~/.local/share/nvim/black
)
To install with vim-plug:
Plug 'psf/black', { 'branch': 'stable' }
or with Vundle:
Plugin 'psf/black'
and execute the following in a terminal:
$ cd ~/.vim/bundle/black
$ git checkout origin/stable -b stable
or you can copy the plugin from plugin/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.vim
Let me know if this requires any changes to work with Vim 8's builtin packadd
, or
Pathogen, and so on.
This plugin requires Vim 7.0+ built with Python 3.6+ support. It needs Python 3.6 to be able to run Black inside 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 installs Black. You can upgrade it later by calling :BlackUpgrade
and
restarting Vim.
If you need to do anything special to make your virtualenv work and install Black (for
example you want to run a version from master), create a virtualenv manually and point
g:black_virtualenv
to it. The plugin will use it.
To run Black on save, add the following line to .vimrc
or init.vim
:
autocmd BufWritePre *.py execute ':Black'
To run Black on 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
. When building Vim from source,
use: ./configure --enable-python3interp=yes
. There's many guides online how to do
this.
I get an import error when using Black from a virtual environment: If you get an error message like this:
Traceback (most recent call last):
File "<string>", line 63, in <module>
File "/home/gui/.vim/black/lib/python3.7/site-packages/black.py", line 45, in <module>
from typed_ast import ast3, ast27
File "/home/gui/.vim/black/lib/python3.7/site-packages/typed_ast/ast3.py", line 40, in <module>
from typed_ast import _ast3
ImportError: /home/gui/.vim/black/lib/python3.7/site-packages/typed_ast/_ast3.cpython-37m-x86_64-linux-gnu.so: undefined symbool: PyExc_KeyboardInterrupt
Then you need to install typed_ast
and regex
directly from the source code. The
error happens because pip
will download Python wheels if
they are available. Python wheels are a new standard of distributing Python packages and
packages that have Cython and extensions written in C are already compiled, so the
installation is much more faster. The problem here is that somehow the Python
environment inside Vim does not match with those already compiled C extensions and these
kind of errors are the result. Luckily there is an easy fix: installing the packages
from the source code.
The two packages that cause the problem are:
Now remove those two packages:
$ pip uninstall regex typed-ast -y
And now you can install them with:
$ pip install --no-binary :all: regex typed-ast
The C extensions will be compiled and now Vim's Python environment will match. Note that
you need to have the GCC compiler and the Python development files installed (on
Ubuntu/Debian do sudo apt-get install build-essential python3-dev
).
If you later want to update Black, you should do it like this:
$ pip install -U black --no-binary regex,typed-ast
Use the Python extension (instructions).
Use sublack plugin.
Use blackcellmagic.
If your editor supports the Language Server Protocol (Atom, Sublime Text, Visual Studio Code and many more), you can use the Python Language Server with the pyls-black plugin.
Use python-black.
Add the following hook to your kakrc, then run black with :format
.
hook global WinSetOption filetype=python %{
set-option window formatcmd 'black -q -'
}
Other editors will require external contributions.
Patches welcome! ✨ 🍰 ✨
Any tool that can pipe code through Black using its stdio mode (just
use -
as the file name).
The formatted code will be returned on stdout (unless --check
was passed). Black
will still emit messages on stderr but that shouldn't affect your use case.
This can be used for example with PyCharm's or IntelliJ's File Watchers.
blackd
is a small HTTP server that exposes Black's functionality over a simple
protocol. The main benefit of using it is to avoid paying the cost of starting up a new
Black process every time you want to blacken a file.
blackd
is not packaged alongside Black by default because it has additional
dependencies. You will need to do pip install black[d]
to install it.
You can start the server on the default port, binding only to the local interface by
running blackd
. You will see a single line mentioning the server's version, and the
host and port it's listening on. blackd
will then print an access log similar to most
web servers on standard output, merged with any exception traces caused by invalid
formatting requests.
blackd
provides even less options than Black. You can see them by running
blackd --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
using curl
:
blackd --bind-port 9090 & # or let blackd choose a port
curl -s -XPOST "localhost:9090" -d "print('valid')"
blackd
only accepts POST
requests at the /
path. The body of the request should
contain the python source code to be formatted, encoded according to the charset
field
in the Content-Type
request header. If no charset
is specified, blackd
assumes
UTF-8
.
There are a few HTTP headers that control how the source is formatted. These correspond
to command line flags for Black. There is one exception to this: X-Protocol-Version
which if present, should have the value 1
, otherwise the request is rejected with
HTTP 501
(Not Implemented).
The headers controlling how code is formatted are:
X-Line-Length
: corresponds to the--line-length
command line flag.X-Skip-String-Normalization
: corresponds to the--skip-string-normalization
command 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
,blackd
will act as Black does when passed the--fast
command line flag.X-Python-Variant
: if set topyi
,blackd
will act as Black does when passed the--pyi
command 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--diff
command line flag. If present, a diff of the formats will be output.
If any of these headers are set to invalid values, blackd
returns a HTTP 400
error
response, mentioning the name of the problematic header in the message body.
Apart from the above, blackd
can 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-Type
header 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 a X-Black-Version
header containing the version of
Black.
black-primer
is a tool built for CI (and huumans) to have Black --check
a number
of (configured in primer.json
) Git accessible projects in parallel. (A PR will be
accepted to add Mercurial support.)
- Ensure we have a
black
+git
in PATH - Load projects from
primer.json
- Run projects in parallel with
--worker
workers (defaults to CPU count / 2)- Checkout projects
- Run black and record result
- Clean up repository checkout (can optionally be disabled via
--keep
)
- Display results summary to screen
- Default to cleaning up
--work-dir
(which defaults to tempfile schemantics) - Return
- 0 for successful run
- < 0 for environment / internal error
-
0 for each project with an error
If you're running locally yourself to test black on lots of code try:
- Using
-k
/--keep
+-w
/--work-dir
so you don't have to re-checkout the repo each run
Usage: black-primer [OPTIONS]
primer - prime projects for blackening ... 🏴
Options:
-c, --config PATH JSON config file path [default: /Users/cooper/repos/
black/src/black_primer/primer.json]
--debug Turn on debug logging [default: False]
-k, --keep Keep workdir + repos post run [default: False]
-L, --long-checkouts Pull big projects to test [default: False]
-R, --rebase Rebase project if already checked out [default:
False]
-w, --workdir PATH Directory Path for repo checkouts [default: /var/fol
ders/tc/hbwxh76j1hn6gqjd2n2sjn4j9k1glp/T/primer.20200
517125229]
-W, --workers INTEGER Number of parallel worker coroutines [default: 69]
-h, --help Show this message and exit.
The config is JSON
format. It's main element is the "projects"
dictionary. Below
explains each parameter:
{
"projects": {
"00_Example": {
"cli_arguments": "List of extra CLI arguments to pass Black for this project",
"expect_formatting_changes": "Boolean to indicate that the version of Black is expected to cause changes",
"git_clone_url": "URL you would pass `git clone` to check out this repo",
"long_checkout": "Boolean to have repo skipped by defauult unless `--long-checkouts` is specified",
"py_versions": "List of major Python versions to run this project with - all will do as you'd expect - run on ALL versions"
},
"aioexabgp": {
"cli_arguments": [],
"expect_formatting_changes": true,
"git_clone_url": "https://github.com/cooperlees/aioexabgp.git",
"long_checkout": false,
"py_versions": ["all", "3.8"] // "all" ignores all other versions
}
}
}
cooper-mbp:black cooper$ ~/venvs/b/bin/black-primer
[2020-05-17 13:06:40,830] INFO: 4 projects to run black over (lib.py:270)
[2020-05-17 13:06:44,215] INFO: Analyzing results (lib.py:285)
-- primer results 📊 --
3 / 4 succeeded (75.0%) ✅
1 / 4 FAILED (25.0%) 💩
- 0 projects Disabled by config
- 0 projects skipped due to Python Version
- 0 skipped due to long checkout
Failed Projects:
## flake8-bugbear:
- Returned 1
- stdout:
--- tests/b303_b304.py 2020-05-17 20:04:09.991227 +0000
+++ tests/b303_b304.py 2020-05-17 20:06:42.753851 +0000
@@ -26,11 +26,11 @@
maxint = 5 # this is okay
# the following shouldn't crash
(a, b, c) = list(range(3))
# it's different than this
a, b, c = list(range(3))
- a, b, c, = list(range(3))
+ a, b, c = list(range(3))
# and different than this
(a, b), c = list(range(3))
a, *b, c = [1, 2, 3, 4, 5]
b[1:3] = [0, 0]
would reformat tests/b303_b304.py
Oh no! 💥 💔 💥
1 file would be reformatted, 22 files would be left unchanged.
Use pre-commit. Once you
have it installed, add this to the
.pre-commit-config.yaml
in your repository:
repos:
- repo: https://github.com/psf/black
rev: stable
hooks:
- id: black
language_version: python3.6
Then run pre-commit install
and you're ready to go.
Avoid using args
in the hook. Instead, store necessary configuration in
pyproject.toml
so that editors and command-line usage of Black all behave consistently
for your project. See Black's own
pyproject.toml for an
example.
If you're already using Python 3.7, switch the language_version
accordingly. Finally,
stable
is a branch that tracks the latest release on PyPI. If you'd rather run on
master, this is also an option.
Black remembers files it has already formatted, unless the --diff
flag is used or
code is passed via standard input. This information is stored per-user. The exact
location of the file depends on the Black version and the system on which Black is
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>.pickle
- macOS:
/Users/<username>/Library/Caches/black/<version>/cache.<line-length>.<file-mode>.pickle
- Linux:
/home/<username>/.cache/black/<version>/cache.<line-length>.<file-mode>.pickle
file-mode
is 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 variable
XDG_CACHE_HOME
to your preferred location. For example, if you want to put the cache
in the directory you're running Black from, set XDG_CACHE_HOME=.cache
. Black will
then write the above files to .cache/black/<version>/
.
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.
The following organizations use Black: Facebook, Dropbox.
Are we missing anyone? Let us know.
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!
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
MIT
In terms of inspiration, Black is about as configurable as gofmt. 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 embrace Black yet. Such changes are unlikely to get accepted. You can still try but prepare to be disappointed.
More details can be found in CONTRIBUTING.
The log's become rather long. It moved to its own file.
See CHANGES.
Glued together by Łukasz Langa.
Maintained with Carol Willing, Carl Meyer, Jelle Zijlstra, Mika Naylor, Zsolt Dollenstein, and Cooper Lees.
Multiple contributions by:
- Abdur-Rahmaan Janhangeer
- Adam Johnson
- Alexander Huynh
- Andrew Thorp
- Andrey
- Andy Freeland
- Anthony Sottile
- Arjaan Buijk
- Artem Malyshev
- Asger Hautop Drewsen
- Augie Fackler
- Aviskar KC
- Benjamin Woodruff
- Brandt Bucher
- Charles Reid
- Christian Heimes
- Chuck Wooters
- Cooper Ry Lees
- Daniel Hahler
- Daniel M. Capella
- Daniele Esposti
- dylanjblack
- Eli Treuherz
- Florent Thiery
- hauntsaninja
- Hugo van Kemenade
- Ivan Katanić
- Jason Fried
- jgirardet
- Joe Antonakakis
- Jon Dufresne
- Jonas Obrist
- Josh Bode
- Juan Luis Cano Rodríguez
- Katie McLaughlin
- Lawrence Chan
- Linus Groh
- Luka Sterbic
- Mariatta
- Matt VanEseltine
- Michael Flaxman
- Michael J. Sullivan
- Michael McClimon
- Miguel Gaiowski
- Mike
- Min ho Kim
- Miroslav Shubernetskiy
- Neraste
- Ofek Lev
- Osaetin Daniel
- Pablo Galindo
- Peter Bengtsson
- pmacosta
- Rishikesh Jha
- Stavros Korokithakis
- Stephen Rosen
- Sunil Kapil
- Thom Lu
- Tom Christie
- Tzu-ping Chung
- Utsav Shah
- vezeli
- Vishwas B Sharma
- Yngve Høiseth
- Yurii Karabas