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The Uncompromising Code Formatter
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> âAny color you like.â
+_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.
-*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.
+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.
-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.
+_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)**
+---
-## Installation and Usage
+## Installation and usage
### Installation
-*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.
+_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}
```
-### Command line options
-
-Black doesn't provide many options. You can list them by running
-`black --help`:
+You can run _Black_ as a package if running it as a script doesn't work:
-```text
-black [OPTIONS] [SRC]...
-
-Options:
- -l, --line-length INTEGER Where to wrap around. [default: 88]
- --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]
- -q, --quiet Don't emit non-error messages to stderr. Errors
- are still emitted, silence those with
- 2>/dev/null.
- --version Show the version and exit.
- --help Show this message and exit.
+```sh
+python -m black {source_file_or_directory}
```
-*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 occured (or `--check` was
- used).
-
+### Command line options
-### NOTE: This is an early pre-release
+_Black_ doesn't provide many options. You can list them by running `black --help`:
-*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**.
+```text
+Usage: black [OPTIONS] [SRC]...
-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``.
+ 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|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.
+```
-## The *Black* code style
+_Black_ is a well-behaved Unix-style command-line tool:
-*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.
+- 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).
+### Using _Black_ with other tools
-### How *Black* wraps lines
+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.
-*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. The coding style used by *Black* can be
-viewed as a strict subset of PEP 8.
+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).
-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:
+### Migrating your code style without ruining git blame
-l = [1,
- 2,
- 3,
-]
+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.
-# out:
+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.
-l = [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.
-```py3
-# in:
-
-l = [[n for n in list_bosses()], [n for n in list_employees()]]
-
-# out:
-
-l = [
- [n for n in list_bosses()], [n for n in list_employees()]
-]
+# Migrate code style to Black
+5b4ab991dede475d393e9d69ec388fd6bd949699
```
-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:
- ...
-```
+Afterwards, you can pass that file to `git blame` and see clean and meaningful blame
+information.
-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).
-
-
-### 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 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'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".
-
-
-### Empty lines
-
-*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.
-
-*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. *Black* will put those empty lines also
-between the function definition and any standalone comments that
-immediately precede the given function. If you want to comment on the
-entire function, use a docstring or put a leading comment in the function
-body.
-
-
-### Trailing commas
-
-*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.
-
-### Strings
-
-*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.
-
-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](https://github.com/ambv/black/issues/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.
+You can even configure `git` to automatically ignore revisions listed in a file on every
+call to `git blame`.
+```console
+$ git config blame.ignoreRevsFile .git-blame-ignore-revs
+```
-## Editor integration
-
-### Emacs
-
-Use [proofit404/blacken](https://github.com/proofit404/blacken).
-
-
-### Vim
-
-Commands and shortcuts:
-
-* `,=` or `: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 to `0`)
-* `g:black_linelength` (defaults to `88`)
-* `g:black_virtualenv` (defaults to `~/.vim/black`)
-
-To install, copy the plugin from [vim/plugin/black.vim](https://github.com/ambv/black/tree/master/vim/plugin/black.vim).
-Let me know if this requires any changes to work with Vim 8's builtin
-`packadd`, or Pathogen, or Vundle, 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.
+**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!)
-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), just
-create a virtualenv manually and point `g:black_virtualenv` to it.
-The plugin will use it.
+### NOTE: This is a beta product
-**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.
+_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.
+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`.
-### Visual Studio Code
+## The _Black_ code style
-Use [joslarson.black-vscode](https://marketplace.visualstudio.com/items?itemName=joslarson.black-vscode).
+_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).
+Please refer to this document before submitting an issue. What seems like a bug might be
+intended behaviour.
-### Other editors
+## Pragmatism
-Atom/Nuclide integration is planned by the author, others will
-require external contributions.
+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.
-Patches welcome! ⨠ð° â¨
+Please refer to this document before submitting an issue just like with the document
+above. What seems like a bug might be intended behaviour.
-Any tool that can pipe code through *Black* using its stdio mode (just
-[use `-` as the file name](http://www.tldp.org/LDP/abs/html/special-chars.html#DASHREF2)).
-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.
+## pyproject.toml
-This can be used for example with PyCharm's [File Watchers](https://www.jetbrains.com/help/pycharm/file-watchers.html).
+_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.
+**Pro-tip**: If you're asking yourself "Do I need to configure anything?" the answer is
+"No". _Black_ is all about sensible defaults.
-## 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/ambv/black
- rev: stable
- hooks:
- - id: black
- args: [--line-length=88, --safe]
- python_version: python3.6
-```
-Then run `pre-commit install` and you're ready to go.
+### What on Earth is a `pyproject.toml` file?
-`args` in the above config is optional but shows you how you can change
-the line length if you really need to. If you're already using Python
-3.7, switch the `python_version` accordingly. Finally, `stable` is a tag
-that is pinned to the latest release on PyPI. If you'd rather run on
-master, this is also an option.
+[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.
-## Testimonials
+### Where _Black_ looks for the file
-**Dusty Phillips**, [writer](https://smile.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dusty+phillips):
+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.
-> Black is opinionated so you don't have to be.
+If you're formatting standard input, _Black_ will look for configuration starting from
+the current working directory.
-**Hynek Schlawack**, [creator of `attrs`](http://www.attrs.org/), core
-developer of Twisted and CPython:
+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:
-> An auto-formatter that doesn't suck is all I want for Xmas!
+- Windows: `~\.black`
+- Unix-like (Linux, MacOS, etc.): `$XDG_CONFIG_HOME/black` (`~/.config/black` if the
+ `XDG_CONFIG_HOME` environment variable is not set)
-**Carl Meyer**, [Django](https://www.djangoproject.com/) core developer:
+Note that these are paths to the TOML file itself (meaning that they shouldn't be named
+as `pyproject.toml`), not directories where you store the configuration. Here, `~`
+refers to the path to your home directory. On Windows, this will be something like
+`C:\\Users\UserName`.
-> At least the name is good.
+You can also explicitly specify the path to a particular file that you want with
+`--config`. In this situation _Black_ will not look for any other file.
-**Kenneth Reitz**, creator of [`requests`](http://python-requests.org/)
-and [`pipenv`](https://docs.pipenv.org/):
+If you're running with `--verbose`, you will see a blue message if a file was found and
+used.
-> This vastly improves the formatting of our code. Thanks a ton!
+Please note `blackd` will not use `pyproject.toml` configuration.
+### Configuration format
-## Show your style
+As the file extension suggests, `pyproject.toml` is a
+[TOML](https://github.com/toml-lang/toml) file. It contains separate sections for
+different tools. _Black_ is using the `[tool.black]` section. The option keys are the
+same as long names of options on the command line.
+
+Note that you have to use single-quoted strings in TOML for regular expressions. It's
+the equivalent of r-strings in Python. Multiline strings are treated as verbose regular
+expressions by Black. Use `[ ]` to denote a significant space character.
-Use the badge in your project's README.md:
+
+Example pyproject.toml
-```markdown
-[](https://github.com/ambv/black)
+```toml
+[tool.black]
+line-length = 88
+target-version = ['py37']
+include = '\.pyi?$'
+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)
+'''
```
-Looks like this: [](https://github.com/ambv/black)
+
+### Lookup hierarchy
-## License
-
-MIT
+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.
-## Contributing to Black
-
-In terms of inspiration, *Black* is about as configurable as *gofmt* and
-*rustfmt* are. 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](CONTRIBUTING.md).
-
-
-## Change Log
-
-### 18.4a1
+## Editor integration
-* added `--quiet` (#78)
+_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).
-* fixed reporting on `--check` with multiple files (#101, #102)
+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).
-### 18.4a0
+## blackd
-* added `--diff` (#87)
+`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.
-* add line breaks before all delimiters, except in cases like commas, to
- better comply with PEP 8 (#73)
+## black-primer
-* standardize string literals to use double quotes (almost) everywhere
- (#75)
+`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.
-* fixed handling of standalone comments within nested bracketed
- expressions; Black will no longer produce super long lines or put all
- standalone comments at the end of the expression (#22)
+(A PR adding Mercurial support will be accepted.)
-* fixed 18.3a4 regression: don't crash and burn on empty lines with
- trailing whitespace (#80)
+## Version control integration
-* fixed 18.3a4 regression: `# yapf: disable` usage as trailing comment
- would cause Black to not emit the rest of the file (#95)
+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:
-* when CTRL+C is pressed while formatting many files, Black no longer
- freaks out with a flurry of asyncio-related exceptions
+```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+
+```
-* only allow up to two empty lines on module level and only single empty
- lines within functions (#74)
+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](https://github.com/psf/black/blob/master/pyproject.toml) for an
+example.
-### 18.3a4
+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.
-* `# fmt: off` and `# fmt: on` are implemented (#5)
+## GitHub Actions
-* automatic detection of deprecated Python 2 forms of print statements
- and exec statements in the formatted file (#49)
+Create a file named `.github/workflows/black.yml` inside your repository with:
-* use proper spaces for complex expressions in default values of typed
- function arguments (#60)
+```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"
+```
-* only return exit code 1 when --check is used (#50)
+### Inputs
-* don't remove single trailing commas from square bracket indexing
- (#59)
+#### `black_args`
-* don't omit whitespace if the previous factor leaf wasn't a math
- operator (#55)
+**optional**: Black input arguments. Defaults to `. --check --diff`.
-* omit extra space in kwarg unpacking if it's the first argument (#46)
+## Ignoring unmodified files
-* omit extra space in [Sphinx auto-attribute comments](http://www.sphinx-doc.org/en/stable/ext/autodoc.html#directive-autoattribute)
- (#68)
+_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\\AppData\Local\black\black\Cache\\cache...pickle`
+- macOS:
+ `/Users//Library/Caches/black//cache...pickle`
+- Linux:
+ `/home//.cache/black//cache...pickle`
-### 18.3a3
+`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.
-* don't remove single empty lines outside of bracketed expressions
- (#19)
+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//`.
-* added ability to pipe formatting from stdin to stdin (#25)
+## Used by
-* restored ability to format code with legacy usage of `async` as
- a name (#20, #42)
+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.
-* even better handling of numpy-style array indexing (#33, again)
+The following organizations use _Black_: Facebook, Dropbox, Mozilla, Quora.
+Are we missing anyone? Let us know.
-### 18.3a2
+## Testimonials
-* 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)
+**Dusty Phillips**,
+[writer](https://smile.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dusty+phillips):
-* ignore empty bracket pairs while splitting. This avoids very weirdly
- looking formattings (#34, #35)
+> _Black_ is opinionated so you don't have to be.
-* remove a trailing comma if there is a single argument to a call
+**Hynek Schlawack**, [creator of `attrs`](https://www.attrs.org/), core developer of
+Twisted and CPython:
-* if top level functions were separated by a comment, don't put four
- empty lines after the upper function
+> An auto-formatter that doesn't suck is all I want for Xmas!
-* fixed unstable formatting of newlines with imports
+**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
+[](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:
+[](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 ð° 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 [Åukasz Langa](mailto:lukasz@langa.pl).
-Maintained with [Carol Willing](mailto:carolcode@willingconsulting.com)
-and [Carl Meyer](mailto:carl@oddbird.net).
+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:
-* [Artem Malyshev](mailto:proofit404@gmail.com)
-* [Daniel M. Capella](mailto:polycitizen@gmail.com)
-* [Eli Treuherz](mailto:eli.treuherz@cgi.com)
-* Hugo van Kemenade
-* [Ivan KataniÄ](mailto:ivan.katanic@gmail.com)
-* [Mika Naylor](mailto:mail@autophagy.io)
-* [Osaetin Daniel](mailto:osaetindaniel@gmail.com)
-* [Zsolt Dollenstein](mailto:zsol.zsol@gmail.com)
+
+- [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 TaÅkaya
+- [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 KataniÄ](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 RodrÃguez](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)