Remove Lowercase Hex (PR #1692) from CHANGES.md (#2133)

[etc/vim.git] / README.md

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-# black
+![Black Logo](https://raw.githubusercontent.com/psf/black/master/docs/_static/logo2-readme.png)

 
 

-[![Build Status](https://travis-ci.org/ambv/black.svg?branch=master)](https://travis-ci.org/ambv/black)
+<h2 align="center">The Uncompromising Code Formatter</h2>

 
 

-> Any color you like.
+<p align="center">
+<a href="https://travis-ci.com/psf/black"><img alt="Build Status" src="https://travis-ci.com/psf/black.svg?branch=master"></a>
+<a href="https://github.com/psf/black/actions"><img alt="Actions Status" src="https://github.com/psf/black/workflows/Test/badge.svg"></a>
+<a href="https://github.com/psf/black/actions"><img alt="Actions Status" src="https://github.com/psf/black/workflows/Primer/badge.svg"></a>
+<a href="https://black.readthedocs.io/en/stable/?badge=stable"><img alt="Documentation Status" src="https://readthedocs.org/projects/black/badge/?version=stable"></a>
+<a href="https://coveralls.io/github/psf/black?branch=master"><img alt="Coverage Status" src="https://coveralls.io/repos/github/psf/black/badge.svg?branch=master"></a>
+<a href="https://github.com/psf/black/blob/master/LICENSE"><img alt="License: MIT" src="https://black.readthedocs.io/en/stable/_static/license.svg"></a>
+<a href="https://pypi.org/project/black/"><img alt="PyPI" src="https://img.shields.io/pypi/v/black"></a>
+<a href="https://pepy.tech/project/black"><img alt="Downloads" src="https://pepy.tech/badge/black"></a>
+<a href="https://anaconda.org/conda-forge/black/"><img alt="conda-forge" src="https://img.shields.io/conda/dn/conda-forge/black.svg?label=conda-forge"></a>
+<a href="https://github.com/psf/black"><img alt="Code style: black" src="https://img.shields.io/badge/code%20style-black-000000.svg"></a>
+</p>

 
 

+> “Any color you like.”

 
 

-*Black* is the uncompromising Python code formatter.  By using it, you
-agree to cease 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.
+_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.
+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.
+_Black_ makes code review faster by producing the smallest diffs possible.

 
 

+Try it out now using the [Black Playground](https://black.now.sh). Watch the
+[PyCon 2019 talk](https://youtu.be/esZLCuWs_2Y) to learn more.

 
 

-## NOTE: This is an early pre-release
+---

 
 

-*Black* can already successfully format itself and the standard library.
-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
-"Alpha" trove classifier, as well as by the "a" 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**.
+_Contents:_ **[Installation and usage](#installation-and-usage)** |
+**[Code style](#the-black-code-style)** | **[Pragmatism](#pragmatism)** |
+**[pyproject.toml](#pyprojecttoml)** | **[Editor integration](#editor-integration)** |
+**[blackd](#blackd)** | **[black-primer](#black-primer)** |
+**[Version control integration](#version-control-integration)** |
+**[GitHub Actions](#github-actions)** |
+**[Ignoring unmodified files](#ignoring-unmodified-files)** | **[Used by](#used-by)** |
+**[Testimonials](#testimonials)** | **[Show your style](#show-your-style)** |
+**[Contributing](#contributing-to-black)** | **[Change log](#change-log)** |
+**[Authors](#authors)**

 
 

-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``.
+---

 
 

+## Installation and usage

 
 

-## Usage
+### Installation

 
 

-*Black* can be installed by running `pip install black`.
+_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]`.

 
 

+#### Install from GitHub
+
+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:
+
+```sh
+black {source_file_or_directory}

 ```
 ```

-black [OPTIONS] [SRC]...
+
+You can run _Black_ as a package if running it as a script doesn't work:
+
+```sh
+python -m black {source_file_or_directory}
+```
+
+### Command line options
+
+_Black_ doesn't provide many options. You can list them by running `black --help`:
+
+```text
+Usage: black [OPTIONS] [SRC]...
+
+  The uncompromising code formatter.

 
 Options:
 
 Options:

-  -l, --line-length INTEGER   Where to wrap around.  [default: 88]
-  --check                     Don't write back the files, just return the
-                              status.  Return code 0 means nothing changed.
-                              Return code 1 means some files were reformatted.
-                              Return code 123 means there was an internal
-                              error.
-  --fast / --safe             If --fast given, skip temporary sanity checks.
-                              [default: --safe]
-  --version                   Show the version and exit.
-  --help                      Show this message and exit.
+  -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|py39]
+                                  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.
+  -C, --skip-magic-trailing-comma
+                                  Don't use trailing commas as a reason to
+                                  split lines.
+
+  --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: /(\.direnv|\.eggs|\.git|\.
+                                  hg|\.mypy_cache|\.nox|\.tox|\.venv|venv|\.sv
+                                  n|_build|buck-out|build|dist)/]
+
+  --extend-exclude TEXT           Like --exclude, but adds additional files
+                                  and directories on top of the excluded
+                                  ones (useful if you simply want to add to
+                                  the default).
+
+  --force-exclude TEXT            Like --exclude, but files and directories
+                                  matching this regex will be excluded even
+                                  when they are passed explicitly as
+                                  arguments.
+
+
+  --stdin-filename TEXT           The name of the file when passing it through
+                                  stdin. Useful to make sure Black will
+                                  respect --force-exclude option on some
+                                  editors that rely on using stdin.
+
+  -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
+                                  exclusion patterns.
+
+  --version                       Show the version and exit.
+  --config FILE                   Read configuration from FILE 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).

 
 

-## The philosophy behind *Black*
+### Using _Black_ with other tools

 
 

-*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`.  It also
-recognizes [YAPF](https://github.com/google/yapf)'s block comments to
-the same effect, as a courtesy for straddling code.
+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](https://pypi.org/p/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](https://github.com/psf/black/blob/master/docs/compatible_configs.md#black-compatible-configurations).

 
 

-### How *Black* formats files
+### Migrating your code style without ruining git blame

 
 

-*Black* ignores previous formatting and applies uniform horizontal
-and vertical whitespace to your code.  The rules for horizontal
-whitespace are pretty obvious and can be summarized as: do whatever
-makes `pycodestyle` happy.
+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](https://git-scm.com/docs/git-blame#Documentation/git-blame.txt---ignore-revltrevgt)
+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.

 
 

-As for vertical whitespace, *Black* tries to render one full expression
-or simple statement per line.  If this fits the allotted line length,
-great.
-```py3
-# in:
-l = [1,
-     2,
-     3,
-]
+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.

 
 

-# out:
-l = [1, 2, 3]
+```
+# Migrate code style to Black
+5b4ab991dede475d393e9d69ec388fd6bd949699

 ```
 
 ```
 

-If not, *Black* will look at the contents of the first outer matching
-brackets and put that in a separate indented line.
-```py3
-# in:
-l = [[n for n in list_bosses()], [n for n in list_employees()]]
+Afterwards, you can pass that file to `git blame` and see clean and meaningful blame
+information.

 
 

-# out:
-l = [
-    [n for n in list_bosses()], [n for n in list_employees()]
-]
+```console
+$ 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)

 ```
 
 ```
 

-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.
-```py3
-# in:
-def very_important_function(template: str, *variables, *, file: os.PathLike, 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,
-    debug: bool = False,
-):
-    """Applies `variables` to the `template` and writes to `file`."""
-    with open(file, 'w') as f:
-        ...
-```
+You can even configure `git` to automatically ignore revisions listed in a file on every
+call to `git blame`.

 
 

-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).
-
-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.
-
-*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.  One exception is control flow statements: *Black* will
-always emit an extra empty line after ``return``, ``raise``, ``break``,
-``continue``, and ``yield``.  This is to make changes in control flow
-more prominent to readers of your code.
-
-That's it.  The rest of the whitespace formatting rules follow PEP 8 and
-are designed to keep `pycodestyle` quiet.
-
-
-### Line length
-
-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](https://youtu.be/wf-BqAjZb8M?t=260).
-
-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](https://github.com/PyCQA/flake8-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:
-```ini
-[flake8]
-max-line-length = 80
-...
-select = C,E,F,W,B,B950
-ignore = E501
+```console
+$ git config blame.ignoreRevsFile .git-blame-ignore-revs

 ```
 
 ```
 

-You'll find *Black*'s own .flake8 config file is configured like this.
-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".
+**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](https://gitlab.com/gitlab-org/gitlab/-/issues/31423) and please let GitHub
+know!)

 
 

+### NOTE: This is a beta product

 
 

-### Editor integration
+_Black_ is already [successfully used](https://github.com/psf/black#used-by) 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.

 
 

-There is currently no integration with any text editors. Vim and
-Atom/Nuclide integration is planned by the author, others will require
-external contributions.
+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`.

 
 

-Patches welcome! ✨ 🍰 ✨
+## The _Black_ code style

 
 

+_Black_ is a PEP 8 compliant opinionated formatter. _Black_ reformats entire files in
+place. It is not configurable. It doesn't take previous formatting into account. Your
+main option of configuring _Black_ is that it doesn't reformat blocks that start with
+`# fmt: off` and end with `# fmt: on`, or lines that ends with `# fmt: skip`. Pay
+attention that `# fmt: on/off` have to be on the same level of indentation. To learn
+more about _Black_'s opinions, to go
+[the_black_code_style](https://github.com/psf/black/blob/master/docs/the_black_code_style.md).

 
 

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

 
 

-**Dusty Phillips**, [writer](https://smile.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dusty+phillips):
+## Pragmatism

 
 

-> Black is opinionated so you don't have to be.
+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](https://github.com/psf/black/blob/master/docs/the_black_code_style.md#pragmatism)
+of `the_black_code_style` describes what those exceptions are and why this is the case.

 
 

-**Hynek Schlawack**, [creator of `attrs`](http://www.attrs.org/), core
-developer of Twisted and CPython:
+Please refer to this document before submitting an issue just like with the document
+above. What seems like a bug might be intended behaviour.

 
 

-> An auto-formatter that doesn't suck is all I want for Xmas!
+## pyproject.toml

 
 

-**Carl Meyer**, [Django](https://www.djangoproject.com/) core developer:
+_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`/`--extend-exclude` patterns for your project.

 
 

-> At least the name is good.
+**Pro-tip**: If you're asking yourself "Do I need to configure anything?" the answer is
+"No". _Black_ is all about sensible defaults.

 
 

-**Kenneth Reitz**, creator of [`requests`](http://python-requests.org/)
-and [`pipenv`](https://docs.pipenv.org/):
+### What on Earth is a `pyproject.toml` file?

 
 

-> This vastly improves the formatting of our code. Thanks a ton!
+[PEP 518](https://www.python.org/dev/peps/pep-0518/) defines `pyproject.toml` as a
+configuration file to store build system requirements for Python projects. With the help
+of tools like [Poetry](https://python-poetry.org/) or
+[Flit](https://flit.readthedocs.io/en/latest/) it can fully replace the need for
+`setup.py` and `setup.cfg` files.
+
+### Where _Black_ looks for the file
+
+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 use a "global" configuration, stored in a specific location in your home
+directory. This will be used as a fallback configuration, that is, it will be used if
+and only if _Black_ doesn't find any configuration as mentioned above. Depending on your
+operating system, this configuration file should be stored as:
+
+- Windows: `~\.black`
+- Unix-like (Linux, MacOS, etc.): `$XDG_CONFIG_HOME/black` (`~/.config/black` if the
+  `XDG_CONFIG_HOME` environment variable is not set)

 
 

+Note that these are paths to the TOML file itself (meaning that they shouldn't be named
+as `pyproject.toml`), not directories where you store the configuration. Here, `~`
+refers to the path to your home directory. On Windows, this will be something like
+`C:\\Users\UserName`.

 
 

-## Tests
+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.

 
 

-Just run:
+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.
+
+### Configuration format
+
+As the file extension suggests, `pyproject.toml` is a
+[TOML](https://github.com/toml-lang/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.
+
+<details>
+<summary>Example <code>pyproject.toml</code></summary>
+
+```toml
+[tool.black]
+line-length = 88
+target-version = ['py37']
+include = '\.pyi?$'
+extend-exclude = '''
+# A regex preceded with ^/ will apply only to files and directories
+# in the root of the project.
+^/foo.py  # exclude a file named foo.py in the root of the project (in addition to the defaults)
+'''

 ```
 ```

-python setup.py test
+
+</details>
+
+### Lookup hierarchy
+
+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.
+
+## Editor integration
+
+_Black_ can be integrated into many editors with plugins. They let you run _Black_ on
+your code with the ease of doing it in your editor. To get started using _Black_ in your
+editor of choice, please see
+[editor_integration](https://github.com/psf/black/blob/master/docs/editor_integration.md).
+
+Patches are welcome for editors without an editor integration or plugin! More
+information can be found in
+[editor_integration](https://github.com/psf/black/blob/master/docs/editor_integration.md#other-editors).
+
+## blackd
+
+`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. Please refer to
+[blackd](https://github.com/psf/black/blob/master/docs/blackd.md) to get the ball
+rolling.
+
+## black-primer
+
+`black-primer` is a tool built for CI (and humans) to have _Black_ `--check` a number of
+(configured in `primer.json`) Git accessible projects in parallel.
+[black_primer](https://github.com/psf/black/blob/master/docs/black_primer.md) has more
+information regarding its usage and configuration.
+
+(A PR adding Mercurial support will be accepted.)
+
+## Version control integration
+
+Use [pre-commit](https://pre-commit.com/). Once you
+[have it installed](https://pre-commit.com/#install), add this to the
+`.pre-commit-config.yaml` in your repository:
+
+```yaml
+repos:
+  - repo: https://github.com/psf/black
+    rev: 20.8b1 # Replace by any tag/version: https://github.com/psf/black/tags
+    hooks:
+      - id: black
+        language_version: python3 # Should be a command that runs python3.6+

 ```
 
 ```
 

-## This tool requires Python 3.6.0+ to run
+Then run `pre-commit install` and you're ready to go.

 
 

-But you can reformat Python 2 code with it, too.  *Black* is able to parse
-all of the new syntax supported on Python 3.6 but also *effectively all*
-the Python 2 syntax at the same time, as long as you're not using print
-statements.
+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](https://github.com/psf/black/blob/master/pyproject.toml) for an
+example.

 
 

-By making the code exclusively Python 3.6+, I'm able to focus on the
-quality of the formatting and re-use all the nice features of the new
-releases (check out [pathlib](https://docs.python.org/3/library/pathlib.html) or
-f-strings) instead of wasting cycles on Unicode compatibility, and so on.
+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.

 
 

+## GitHub Actions

 
 

-## License
+Create a file named `.github/workflows/black.yml` inside your repository with:

 
 

-MIT
+```yaml
+name: Lint
+
+on: [push, pull_request]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+      - uses: psf/black@stable
+        with:
+          args: ". --check"
+```

 
 

+### Inputs

 
 

-## Contributing
+#### `black_args`

 
 

-In terms of inspiration, *Black* is about as configurable as *gofmt* and
-*rustfmt* are.  This is deliberate.
+**optional**: Black input arguments. Defaults to `. --check --diff`.

 
 

-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.
+## Ignoring unmodified files

 
 

-More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
+_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`

 
 

-## Change Log
+`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.

 
 

-### 18.3a2 (unreleased)
+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>/`.

 
 

-* changed positioning of binary operators to occur at beginning of lines
-  instead of at the end, following [a recent change to PEP8](https://github.com/python/peps/commit/c59c4376ad233a62ca4b3a6060c81368bd21e85b)
-  (#21)
+## Used by

 
 

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

 
 

-* remove a trailing comma if there is a single argument to a call
+The following organizations use _Black_: Facebook, Dropbox, Mozilla, Quora.

 
 

-* if top level functions were separated by a comment, don't put four
-  empty lines after the upper function
+Are we missing anyone? Let us know.

 
 

-* fixed unstable formatting of newlines with imports
+## Testimonials
+
+**Dusty Phillips**,
+[writer](https://smile.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dusty+phillips):
+
+> _Black_ is opinionated so you don't have to be.
+
+**Hynek Schlawack**, [creator of `attrs`](https://www.attrs.org/), core developer of
+Twisted and CPython:
+
+> An auto-formatter that doesn't suck is all I want for Xmas!
+
+**Carl Meyer**, [Django](https://www.djangoproject.com/) core developer:

 
 

-* fixed unintentional folding of post scriptum standalone comments
-  into last statement if it was a simple statement (#18, #28)
+> At least the name is good.

 
 

-* fixed missing space in numpy-style array indexing (#33)
+**Kenneth Reitz**, creator of [`requests`](http://python-requests.org/) and
+[`pipenv`](https://readthedocs.org/projects/pipenv/):

 
 

-* fixed spurious space after star-based unary expressions (#31)
+> This vastly improves the formatting of our code. Thanks a ton!

 
 

+## Show your style

 
 

-### 18.3a1
+Use the badge in your project's README.md:

 
 

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

 
 

-* 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)
+Using the badge in README.rst:

 
 

-* fixed invalid spacing of dots in relative imports (#6, #13)
+```
+.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
+    :target: https://github.com/psf/black
+```

 
 

-* fixed invalid splitting after comma on unpacked variables in for-loops
-  (#23)
+Looks like this:
+[![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)

 
 

-* fixed spurious space in parenthesized set expressions (#7)
+## License

 
 

-* fixed spurious space after opening parentheses and in default
-  arguments (#14, #17)
+MIT

 
 

-* fixed spurious space after unary operators when the operand was
-  a complex expression (#15)
+## Contributing to _Black_

 
 

+In terms of inspiration, _Black_ is about as configurable as _gofmt_. This is
+deliberate.

 
 

-### 18.3a0
+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.

 
 

-* first published version, Happy 🍰 Day 2018!
+More details can be found in
+[CONTRIBUTING](https://github.com/psf/black/blob/master/CONTRIBUTING.md).

 
 

-* alpha quality
+## Change log

 
 

-* date-versioned (see: https://calver.org/)
+The log's become rather long. It moved to its own file.

 
 

+See [CHANGES](https://github.com/psf/black/blob/master/CHANGES.md).

 
 ## Authors
 
 Glued together by [Łukasz Langa](mailto:lukasz@langa.pl).
 
 ## Authors
 
 Glued together by [Łukasz Langa](mailto:lukasz@langa.pl).

+
+Maintained with [Carol Willing](mailto:carolcode@willingconsulting.com),
+[Carl Meyer](mailto:carl@oddbird.net),
+[Jelle Zijlstra](mailto:jelle.zijlstra@gmail.com),
+[Mika Naylor](mailto:mail@autophagy.io),
+[Zsolt Dollenstein](mailto:zsol.zsol@gmail.com), and
+[Cooper Lees](mailto:me@cooperlees.com).
+
+Multiple contributions by:
+
+- [Abdur-Rahmaan Janhangeer](mailto:arj.python@gmail.com)
+- [Adam Johnson](mailto:me@adamj.eu)
+- [Adam Williamson](mailto:adamw@happyassassin.net)
+- [Alexander Huynh](mailto:github@grande.coffee)
+- [Alex Vandiver](mailto:github@chmrr.net)
+- [Allan Simon](mailto:allan.simon@supinfo.com)
+- Anders-Petter Ljungquist
+- [Andrew Thorp](mailto:andrew.thorp.dev@gmail.com)
+- [Andrew Zhou](mailto:andrewfzhou@gmail.com)
+- [Andrey](mailto:dyuuus@yandex.ru)
+- [Andy Freeland](mailto:andy@andyfreeland.net)
+- [Anthony Sottile](mailto:asottile@umich.edu)
+- [Arjaan Buijk](mailto:arjaan.buijk@gmail.com)
+- [Arnav Borbornah](mailto:arnavborborah11@gmail.com)
+- [Artem Malyshev](mailto:proofit404@gmail.com)
+- [Asger Hautop Drewsen](mailto:asgerdrewsen@gmail.com)
+- [Augie Fackler](mailto:raf@durin42.com)
+- [Aviskar KC](mailto:aviskarkc10@gmail.com)
+- Batuhan Taşkaya
+- [Benjamin Wohlwend](mailto:bw@piquadrat.ch)
+- [Benjamin Woodruff](mailto:github@benjam.info)
+- [Bharat Raghunathan](mailto:bharatraghunthan9767@gmail.com)
+- [Brandt Bucher](mailto:brandtbucher@gmail.com)
+- [Brett Cannon](mailto:brett@python.org)
+- [Bryan Bugyi](mailto:bryan.bugyi@rutgers.edu)
+- [Bryan Forbes](mailto:bryan@reigndropsfall.net)
+- [Calum Lind](mailto:calumlind@gmail.com)
+- [Charles](mailto:peacech@gmail.com)
+- Charles Reid
+- [Christian Clauss](mailto:cclauss@bluewin.ch)
+- [Christian Heimes](mailto:christian@python.org)
+- [Chuck Wooters](mailto:chuck.wooters@microsoft.com)
+- [Chris Rose](mailto:offline@offby1.net)
+- Codey Oxley
+- [Cong](mailto:congusbongus@gmail.com)
+- [Cooper Ry Lees](mailto:me@cooperlees.com)
+- [Dan Davison](mailto:dandavison7@gmail.com)
+- [Daniel Hahler](mailto:github@thequod.de)
+- [Daniel M. Capella](mailto:polycitizen@gmail.com)
+- Daniele Esposti
+- [David Hotham](mailto:david.hotham@metaswitch.com)
+- [David Lukes](mailto:dafydd.lukes@gmail.com)
+- [David Szotten](mailto:davidszotten@gmail.com)
+- [Denis Laxalde](mailto:denis@laxalde.org)
+- [Douglas Thor](mailto:dthor@transphormusa.com)
+- dylanjblack
+- [Eli Treuherz](mailto:eli@treuherz.com)
+- [Emil Hessman](mailto:emil@hessman.se)
+- [Felix Kohlgrüber](mailto:felix.kohlgrueber@gmail.com)
+- [Florent Thiery](mailto:fthiery@gmail.com)
+- Francisco
+- [Giacomo Tagliabue](mailto:giacomo.tag@gmail.com)
+- [Greg Gandenberger](mailto:ggandenberger@shoprunner.com)
+- [Gregory P. Smith](mailto:greg@krypto.org)
+- Gustavo Camargo
+- hauntsaninja
+- [Hadi Alqattan](mailto:alqattanhadizaki@gmail.com)
+- [Heaford](mailto:dan@heaford.com)
+- [Hugo Barrera](mailto::hugo@barrera.io)
+- Hugo van Kemenade
+- [Hynek Schlawack](mailto:hs@ox.cx)
+- [Ivan Katanić](mailto:ivan.katanic@gmail.com)
+- [Jakub Kadlubiec](mailto:jakub.kadlubiec@skyscanner.net)
+- [Jakub Warczarek](mailto:jakub.warczarek@gmail.com)
+- [Jan Hnátek](mailto:jan.hnatek@gmail.com)
+- [Jason Fried](mailto:me@jasonfried.info)
+- [Jason Friedland](mailto:jason@friedland.id.au)
+- [jgirardet](mailto:ijkl@netc.fr)
+- Jim Brännlund
+- [Jimmy Jia](mailto:tesrin@gmail.com)
+- [Joe Antonakakis](mailto:jma353@cornell.edu)
+- [Jon Dufresne](mailto:jon.dufresne@gmail.com)
+- [Jonas Obrist](mailto:ojiidotch@gmail.com)
+- [Jonty Wareing](mailto:jonty@jonty.co.uk)
+- [Jose Nazario](mailto:jose.monkey.org@gmail.com)
+- [Joseph Larson](mailto:larson.joseph@gmail.com)
+- [Josh Bode](mailto:joshbode@fastmail.com)
+- [Josh Holland](mailto:anowlcalledjosh@gmail.com)
+- [Joshua Cannon](mailto:joshdcannon@gmail.com)
+- [José Padilla](mailto:jpadilla@webapplicate.com)
+- [Juan Luis Cano Rodríguez](mailto:hello@juanlu.space)
+- [kaiix](mailto:kvn.hou@gmail.com)
+- [Katie McLaughlin](mailto:katie@glasnt.com)
+- Katrin Leinweber
+- [Keith Smiley](mailto:keithbsmiley@gmail.com)
+- [Kenyon Ralph](mailto:kenyon@kenyonralph.com)
+- [Kevin Kirsche](mailto:Kev.Kirsche+GitHub@gmail.com)
+- [Kyle Hausmann](mailto:kyle.hausmann@gmail.com)
+- [Kyle Sunden](mailto:sunden@wisc.edu)
+- Lawrence Chan
+- [Linus Groh](mailto:mail@linusgroh.de)
+- [Loren Carvalho](mailto:comradeloren@gmail.com)
+- [Luka Sterbic](mailto:luka.sterbic@gmail.com)
+- [LukasDrude](mailto:mail@lukas-drude.de)
+- Mahmoud Hossam
+- Mariatta
+- [Matt VanEseltine](mailto:vaneseltine@gmail.com)
+- [Matthew Clapp](mailto:itsayellow+dev@gmail.com)
+- [Matthew Walster](mailto:matthew@walster.org)
+- Max Smolens
+- [Michael Aquilina](mailto:michaelaquilina@gmail.com)
+- [Michael Flaxman](mailto:michael.flaxman@gmail.com)
+- [Michael J. Sullivan](mailto:sully@msully.net)
+- [Michael McClimon](mailto:michael@mcclimon.org)
+- [Miguel Gaiowski](mailto:miggaiowski@gmail.com)
+- [Mike](mailto:roshi@fedoraproject.org)
+- [mikehoyio](mailto:mikehoy@gmail.com)
+- [Min ho Kim](mailto:minho42@gmail.com)
+- [Miroslav Shubernetskiy](mailto:miroslav@miki725.com)
+- MomIsBestFriend
+- [Nathan Goldbaum](mailto:ngoldbau@illinois.edu)
+- [Nathan Hunt](mailto:neighthan.hunt@gmail.com)
+- [Neraste](mailto:neraste.herr10@gmail.com)
+- [Nikolaus Waxweiler](mailto:madigens@gmail.com)
+- [Ofek Lev](mailto:ofekmeister@gmail.com)
+- [Osaetin Daniel](mailto:osaetindaniel@gmail.com)
+- [otstrel](mailto:otstrel@gmail.com)
+- [Pablo Galindo](mailto:Pablogsal@gmail.com)
+- [Paul Ganssle](mailto:p.ganssle@gmail.com)
+- [Paul Meinhardt](mailto:mnhrdt@gmail.com)
+- [Peter Bengtsson](mailto:mail@peterbe.com)
+- [Peter Grayson](mailto:pete@jpgrayson.net)
+- [Peter Stensmyr](mailto:peter.stensmyr@gmail.com)
+- pmacosta
+- [Quentin Pradet](mailto:quentin@pradet.me)
+- [Ralf Schmitt](mailto:ralf@systemexit.de)
+- [Ramón Valles](mailto:mroutis@protonmail.com)
+- [Richard Fearn](mailto:richardfearn@gmail.com)
+- Richard Si
+- [Rishikesh Jha](mailto:rishijha424@gmail.com)
+- [Rupert Bedford](mailto:rupert@rupertb.com)
+- Russell Davis
+- [Rémi Verschelde](mailto:rverschelde@gmail.com)
+- [Sami Salonen](mailto:sakki@iki.fi)
+- [Samuel Cormier-Iijima](mailto:samuel@cormier-iijima.com)
+- [Sanket Dasgupta](mailto:sanketdasgupta@gmail.com)
+- Sergi
+- [Scott Stevenson](mailto:scott@stevenson.io)
+- Shantanu
+- [shaoran](mailto:shaoran@sakuranohana.org)
+- [Shinya Fujino](mailto:shf0811@gmail.com)
+- springstan
+- [Stavros Korokithakis](mailto:hi@stavros.io)
+- [Stephen Rosen](mailto:sirosen@globus.org)
+- [Steven M. Vascellaro](mailto:S.Vascellaro@gmail.com)
+- [Sunil Kapil](mailto:snlkapil@gmail.com)
+- [Sébastien Eustace](mailto:sebastien.eustace@gmail.com)
+- [Tal Amuyal](mailto:TalAmuyal@gmail.com)
+- [Terrance](mailto:git@terrance.allofti.me)
+- [Thom Lu](mailto:thomas.c.lu@gmail.com)
+- [Thomas Grainger](mailto:tagrain@gmail.com)
+- [Tim Gates](mailto:tim.gates@iress.com)
+- [Tim Swast](mailto:swast@google.com)
+- [Timo](mailto:timo_tk@hotmail.com)
+- Toby Fleming
+- [Tom Christie](mailto:tom@tomchristie.com)
+- [Tony Narlock](mailto:tony@git-pull.com)
+- [Tsuyoshi Hombashi](mailto:tsuyoshi.hombashi@gmail.com)
+- [Tushar Chandra](mailto:tusharchandra2018@u.northwestern.edu)
+- [Tzu-ping Chung](mailto:uranusjr@gmail.com)
+- [Utsav Shah](mailto:ukshah2@illinois.edu)
+- utsav-dbx
+- vezeli
+- [Ville Skyttä](mailto:ville.skytta@iki.fi)
+- [Vishwas B Sharma](mailto:sharma.vishwas88@gmail.com)
+- [Vlad Emelianov](mailto:volshebnyi@gmail.com)
+- [williamfzc](mailto:178894043@qq.com)
+- [wouter bolsterlee](mailto:wouter@bolsterl.ee)
+- Yazdan
+- [Yngve Høiseth](mailto:yngve@hoiseth.net)
+- [Yurii Karabas](mailto:1998uriyyo@gmail.com)
+- [Zac Hatfield-Dodds](mailto:zac@zhd.dev)