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

The Uncompromising Code Formatter

> “Any color you like.” _Black_ is the uncompromising Python code formatter. By using it, you agree to cede control over minutiae of hand-formatting. In return, _Black_ gives you speed, determinism, and freedom from `pycodestyle` nagging about formatting. You will save time and mental energy for more important matters. Blackened code looks the same regardless of the project you're reading. Formatting becomes transparent after a while and you can focus on the content instead. _Black_ makes code review faster by producing the smallest diffs possible. Try it out now using the [Black Playground](https://black.now.sh). Watch the [PyCon 2019 talk](https://youtu.be/esZLCuWs_2Y) to learn more. --- _Contents:_ **[Installation and usage](#installation-and-usage)** | **[Code style](#the-black-code-style)** | **[Pragmatism](#pragmatism)** **[pyproject.toml](#pyprojecttoml)** | **[Editor integration](#editor-integration)** | **[blackd](#blackd)** | **[Version control integration](#version-control-integration)** | **[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 _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. ### Usage To get started right away with sensible defaults: ``` black {source_file_or_directory} ``` ### Command line options _Black_ doesn't provide many options. You can list them by running `black --help`: ```text black [OPTIONS] [SRC]... Options: -c, --code TEXT Format the code passed in as a string. -l, --line-length INTEGER How many characters per line to allow. [default: 88] -t, --target-version [py27|py33|py34|py35|py36|py37|py38] Python versions that should be supported by Black's output. [default: per-file auto- detection] --py36 Allow using Python 3.6-only syntax on all input files. This will put trailing commas in function signatures and calls also after *args and **kwargs. Deprecated; use --target-version instead. [default: per-file auto-detection] --pyi Format all input files like typing stubs regardless of file extension (useful when piping source on standard input). -S, --skip-string-normalization Don't normalize string quotes or prefixes. --check Don't write the files back, just return the status. Return code 0 means nothing would change. Return code 1 means some files would be reformatted. Return code 123 means there was an internal error. --diff Don't write the files back, just output a diff for each file on stdout. --fast / --safe If --fast given, skip temporary sanity checks. [default: --safe] --include TEXT A regular expression that matches files and directories that should be included on recursive searches. An empty value means all files are included regardless of the name. Use forward slashes for directories on all platforms (Windows, too). Exclusions are calculated first, inclusions later. [default: \.pyi?$] --exclude TEXT A regular expression that matches files and directories that should be excluded on recursive searches. An empty value means no paths are excluded. Use forward slashes for directories on all platforms (Windows, too). Exclusions are calculated first, inclusions later. [default: /(\.eggs|\.git|\.hg|\.mypy _cache|\.nox|\.tox|\.venv|_build|buck- out|build|dist)/] -q, --quiet Don't emit non-error messages to stderr. Errors are still emitted, silence those with 2>/dev/null. -v, --verbose Also emit messages to stderr about files that were not changed or were ignored due to --exclude=. --version Show the version and exit. --config PATH Read configuration from PATH. -h, --help Show this message and exit. ``` _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). ### NOTE: This is a beta product _Black_ is already [successfully used](#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`. ## The _Black_ code style _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](https://github.com/google/yapf)'s block comments to the same effect, as a courtesy for straddling code. ### How _Black_ wraps lines _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. ```py3 # 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. ```py3 # 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. ```py3 # 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: ... ``` 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](https://pypi.org/p/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 ] ```

### 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 = 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](https://github.com/PyCQA/flake8-bugbear#opinionated-warnings) 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:** ```ini [flake8] max-line-length = 88 extend-ignore = E203 ``` ### 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. _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](https://www.python.org/dev/peps/pep-0257/#multi-line-docstrings). _Black_ won't insert empty lines after function docstrings unless that empty line is required due to an inner function starting immediately after. ### 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. _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](https://github.com/psf/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](https://www.python.org/dev/peps/pep-0257/#what-is-a-docstring). 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"](https://stackoverflow.com/a/56190)), you can pass `--skip-string-normalization` on the command line. This is meant as an adoption helper, avoid using this for new projects. ### Numeric literals _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`. ### Line breaks & binary operators _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](https://www.python.org/dev/peps/pep-0008/#should-a-line-break-before-or-after-a-binary-operator) 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. ### Slices PEP 8 [recommends](https://www.python.org/dev/peps/pep-0008/#whitespace-in-expressions-and-statements) 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 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. ### Parentheses 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: ```py3 return not (this or that) decision = (maybe.this() and values > 0) or (maybe.that() and values < 0) ``` ### Call chains Some popular APIs, like ORMs, use call chaining. This API style is known as a [fluent interface](https://en.wikipedia.org/wiki/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: ```py3 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() ) ``` ### Typing stub files 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](https://www.python.org/dev/peps/pep-0484/#stub-files) 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 `...` over `pass`; - 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`, use `Optional[]` explicitly; - use `float` instead of `Union[int, float]`. ## Pragmatism Early versions of _Black_ used to be absolutist in some respects. They took after its initial author. This was fine at the time as it made the implementation simpler and there were not many users anyway. Not many edge cases were reported. As a mature tool, _Black_ does make some exceptions to rules it otherwise holds. This section documents what those exceptions are and why this is the case. ### The magic trailing comma _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: ```py3 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. ### r"strings" and R"strings" _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](https://github.com/MagicStack/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. ## pyproject.toml _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. ### What on Earth is a `pyproject.toml` file? [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://poetry.eustace.io/) 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 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. ### 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.

Example `pyproject.toml`

### 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 ### Emacs Use [proofit404/blacken](https://github.com/proofit404/blacken) or [Elpy](https://github.com/jorgenschaefer/elpy). ### PyCharm/IntelliJ IDEA 1. Install `black`. ```console $ pip install black ``` 2. Locate your `black` installation folder. On macOS / Linux / BSD: ```console $ which black /usr/local/bin/black # possible location ``` On Windows: ```console $ where black %LocalAppData%\Programs\Python\Python36-32\Scripts\black.exe # possible location ``` 3. Open External tools in PyCharm/IntelliJ IDEA On macOS: `PyCharm -> Preferences -> Tools -> External Tools` On Windows / Linux / BSD: `File -> Settings -> Tools -> External Tools` 4. Click the + icon to add a new external tool with the following values: - Name: Black - Description: Black is the uncompromising Python code formatter. - Program: - Arguments: `"$FilePath$"` 5. 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`. 6. Optionally, run _Black_ on every file save: 1. Make sure you have the [File Watcher](https://plugins.jetbrains.com/plugin/7177-file-watchers) plugin installed. 2. Go to `Preferences or Settings -> Tools -> File Watchers` and click `+` to add a new watcher: - Name: Black - File type: Python - Scope: Project Files - Program: - Arguments: `$FilePath$` - Output paths to refresh: `$FilePath$` - Working directory: `$ProjectFileDir$` - Uncheck "Auto-save edited files to trigger the watcher" ### Wing IDE Wing supports black via the OS Commands tool, as explained in the Wing documentation on [pep8 formatting](https://wingware.com/doc/edit/pep8). The detailed procedure is: 1. Install `black`. ```console $ pip install black ``` 2. Make sure it runs from the command line, e.g. ```console $ black --help ``` 3. 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 - [x] Raise OS Commands when executed - [x] Auto-save files before execution - [x] Line mode 4. Select a file in the editor and press **F1** , or whatever key binding you selected in step 3, to reformat the file. ### Vim 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 to `0`) - `g:black_linelength` (defaults to `88`) - `g:black_skip_string_normalization` (defaults to `0`) - `g:black_virtualenv` (defaults to `~/.vim/black` or `~/.local/share/nvim/black`) To install with [vim-plug](https://github.com/junegunn/vim-plug): ``` Plug 'psf/black' ``` or with [Vundle](https://github.com/VundleVim/Vundle.vim): ``` Plugin 'psf/black' ``` or you can copy the plugin from [plugin/black.vim](https://github.com/psf/black/tree/master/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 :Black ``` **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. ### Visual Studio Code Use the [Python extension](https://marketplace.visualstudio.com/items?itemName=ms-python.python) ([instructions](https://code.visualstudio.com/docs/python/editing#_formatting)). ### SublimeText 3 Use [sublack plugin](https://github.com/jgirardet/sublack). ### Jupyter Notebook Magic Use [blackcellmagic](https://github.com/csurfer/blackcellmagic). ### Python Language Server If your editor supports the [Language Server Protocol](https://langserver.org/) (Atom, Sublime Text, Visual Studio Code and many more), you can use the [Python Language Server](https://github.com/palantir/python-language-server) with the [pyls-black](https://github.com/rupert/pyls-black) plugin. ### Atom/Nuclide Use [python-black](https://atom.io/packages/python-black). ### Kakoune Add the following hook to your kakrc, then run black with `:format`. ``` hook global WinSetOption filetype=python %{ set-option window formatcmd 'black -q -' } ``` ### Thonny Use [Thonny-black-code-format](https://github.com/Franccisco/thonny-black-code-format). ### Other editors 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](https://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. This can be used for example with PyCharm's or IntelliJ's [File Watchers](https://www.jetbrains.com/help/pycharm/file-watchers.html). ## 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. ### Usage `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`: ```text 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')" ``` ### Protocol `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 to `fast`, `blackd` will act as _Black_ does when passed the `--fast` command line flag. - `X-Python-Variant`: if set to `pyi`, `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 with `py`. For example, to request code that is compatible with Python 3.5 and 3.6, set the header to `py3.5,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 the `Content-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_. ## 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: 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](https://github.com/psf/black/blob/master/pyproject.toml) for an example. If you're already using Python 3.7, switch the `language_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. ## Ignoring unmodified files _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` `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//`. ## Used by The following notable open-source projects trust _Black_ with enforcing a consistent code style: pytest, tox, Pyramid, Django Channels, Hypothesis, attrs, SQLAlchemy, Poetry, PyPA applications (Warehouse, Pipenv, virtualenv), pandas, Pillow, every Datadog Agent Integration, Home Assistant. Are we missing anyone? Let us know. ## 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: > At least the name is good. **Kenneth Reitz**, creator of [`requests`](http://python-requests.org/) and [`pipenv`](https://docs.pipenv.org/): > This vastly improves the formatting of our code. Thanks a ton! ## Show your style Use the badge in your project's README.md: ```markdown [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black) ``` Using the badge in README.rst: ``` .. image:: https://img.shields.io/badge/code%20style-black-000000.svg :target: https://github.com/psf/black ``` Looks like this: [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black) ## License MIT ## Contributing to _Black_ 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](CONTRIBUTING.md). ## Change Log The log's become rather long. It moved to its own file. See [CHANGES](CHANGES.md). ## 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) - [Alexander Huynh](mailto:github@grande.coffee) - [Andrew Thorp](mailto:andrew.thorp.dev@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) - [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) - [Benjamin Woodruff](mailto:github@benjam.info) - [Brandt Bucher](mailto:brandtbucher@gmail.com) - Charles Reid - [Christian Heimes](mailto:christian@python.org) - [Chuck Wooters](mailto:chuck.wooters@microsoft.com) - [Cooper Ry Lees](mailto:me@cooperlees.com) - [Daniel Hahler](mailto:github@thequod.de) - [Daniel M. Capella](mailto:polycitizen@gmail.com) - Daniele Esposti - dylanjblack - [Eli Treuherz](mailto:eli@treuherz.com) - [Florent Thiery](mailto:fthiery@gmail.com) - hauntsaninja - Hugo van Kemenade - [Ivan Katanić](mailto:ivan.katanic@gmail.com) - [Jason Fried](mailto:me@jasonfried.info) - [jgirardet](mailto:ijkl@netc.fr) - [Joe Antonakakis](mailto:jma353@cornell.edu) - [Jon Dufresne](mailto:jon.dufresne@gmail.com) - [Jonas Obrist](mailto:ojiidotch@gmail.com) - [Josh Bode](mailto:joshbode@fastmail.com) - [Juan Luis Cano Rodríguez](mailto:hello@juanlu.space) - [Katie McLaughlin](mailto:katie@glasnt.com) - Lawrence Chan - [Linus Groh](mailto:mail@linusgroh.de) - [Luka Sterbic](mailto:luka.sterbic@gmail.com) - Mariatta - [Matt VanEseltine](mailto:vaneseltine@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) - [Min ho Kim](mailto:minho42@gmail.com) - [Miroslav Shubernetskiy](mailto:miroslav@miki725.com) - [Neraste](mailto:neraste.herr10@gmail.com) - [Ofek Lev](mailto:ofekmeister@gmail.com) - [Osaetin Daniel](mailto:osaetindaniel@gmail.com) - [Pablo Galindo](mailto:Pablogsal@gmail.com) - [Peter Bengtsson](mailto:mail@peterbe.com) - pmacosta - [Rishikesh Jha](mailto:rishijha424@gmail.com) - [Stavros Korokithakis](mailto:hi@stavros.io) - [Stephen Rosen](mailto:sirosen@globus.org) - [Sunil Kapil](mailto:snlkapil@gmail.com) - [Thom Lu](mailto:thomas.c.lu@gmail.com) - [Tom Christie](mailto:tom@tomchristie.com) - [Tzu-ping Chung](mailto:uranusjr@gmail.com) - [Utsav Shah](mailto:ukshah2@illinois.edu) - vezeli - [Vishwas B Sharma](mailto:sharma.vishwas88@gmail.com) - [Yngve Høiseth](mailto:yngve@hoiseth.net) - [Yurii Karabas](mailto:1998uriyyo@gmail.com)