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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.vercel.app). 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.
+**[Read the documentation on ReadTheDocs!](https://black.readthedocs.io/en/stable)**
+---
-## 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]`. If you want to format Jupyter Notebooks, install with
+`pip install black[jupyter]`.
+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`:
-
-```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]
- --version Show the version and exit.
- --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 occured (or `--check` was
- used).
-
-
-### 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**.
-
-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`. 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 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.
-
-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,
-]
-
-# out:
-
-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:
+You can run _Black_ as a package if running it as a script doesn't work:
-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()]
-]
-```
-
-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 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
+```sh
+python -m black {source_file_or_directory}
```
-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.
-
+Further information can be found in our docs:
-### Trailing commas
+- [Usage and Configuration](https://black.readthedocs.io/en/stable/usage_and_configuration/index.html)
-*Black* will add trailing commas to expressions that are split
-by comma where each element is on its own line. This includes function
-signatures.
+### NOTE: This is a beta product
-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.
+_Black_ is already [successfully used](https://github.com/psf/black#used-by) by many
+projects, small and big. Black has a comprehensive test suite, with efficient parallel
+tests, and our own auto formatting and parallel Continuous Integration runner. However,
+_Black_ is still beta. 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.
-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, ]```.
+Also, as a safety measure which slows down processing, _Black_ will check that the
+reformatted code still produces a valid AST that is effectively equivalent to the
+original (see the
+[Pragmatism](https://black.readthedocs.io/en/stable/the_black_code_style/current_style.html#ast-before-and-after-formatting)
+section for details). If you're feeling confident, use `--fast`.
-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.
+## The _Black_ code style
-### Strings
+_Black_ is a PEP 8 compliant opinionated formatter. _Black_ reformats entire files in
+place. Style configuration options are deliberately limited and rarely added. It doesn't
+take previous formatting into account (see [Pragmatism](#pragmatism) for exceptions).
-*Black* prefers double quotes (`"` and `"""`), but only if this does not
-result in more escaping. It will remove escape sequences as necessary as
-part of moving to the other type of quote. This applies to all kinds of
-prefixed strings, including *raw-strings* (`r""`), *byte literals* (`b""`),
-and *formatted strings* (`f""`). The approach above strikes a good balance
-between consistency and legibility.
+Our documentation covers the current _Black_ code style, but planned changes to it are
+also documented. They're both worth taking a look:
+- [The _Black_ Code Style: Current style](https://black.readthedocs.io/en/stable/the_black_code_style/current_style.html)
+- [The _Black_ Code Style: Future style](https://black.readthedocs.io/en/stable/the_black_code_style/future_style.html)
-## Editor integration
+Please refer to this document before submitting an issue. What seems like a bug might be
+intended behaviour.
-### Emacs
+### Pragmatism
-Use [proofit404/blacken](https://github.com/proofit404/blacken).
+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.
+- [The _Black_ code style: Pragmatism](https://black.readthedocs.io/en/stable/the_black_code_style/current_style.html#pragmatism)
-### Vim
+Please refer to this document before submitting an issue just like with the document
+above. What seems like a bug might be intended behaviour.
-Commands and shortcuts:
+## Configuration
-* `,=` 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.
+_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`/`--force-exclude`/`--extend-exclude` patterns for your
+project.
-Configuration:
-* `g:black_fast` (defaults to `0`)
-* `g:black_linelength` (defaults to `88`)
-* `g:black_virtualenv` (defaults to `~/.vim/black`)
+You can find more details in our documentation:
-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.
+- [The basics: Configuration via a file](https://black.readthedocs.io/en/stable/usage_and_configuration/the_basics.html#configuration-via-a-file)
-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.
+And if you're looking for more general configuration documentation:
-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.
+- [Usage and Configuration](https://black.readthedocs.io/en/stable/usage_and_configuration/index.html)
-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.
+**Pro-tip**: If you're asking yourself "Do I need to configure anything?" the answer is
+"No". _Black_ is all about sensible defaults. Applying those defaults will have your
+code in compliance with many other _Black_ formatted projects.
-**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.
+## 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, Bandersnatch, Pipenv, virtualenv), pandas, Pillow,
+Twisted, LocalStack, every Datadog Agent Integration, Home Assistant, Zulip, Kedro, and
+many more.
-### Visual Studio Code
+The following organizations use _Black_: Facebook, Dropbox, Mozilla, Quora, Duolingo,
+QuantumBlack.
-Use [joslarson.black-vscode](https://marketplace.visualstudio.com/items?itemName=joslarson.black-vscode).
+Are we missing anyone? Let us know.
+## Testimonials
-### Other editors
-
-Atom/Nuclide integration is planned by the author, others will
-require external contributions.
-
-Patches welcome! ⨠ð° â¨
-
-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.
-
-This can be used for example with PyCharm's [File Watchers](https://www.jetbrains.com/help/pycharm/file-watchers.html).
+**Mike Bayer**, [author of `SQLAlchemy`](https://www.sqlalchemy.org/):
+> I can't think of any single tool in my entire programming career that has given me a
+> bigger productivity increase by its introduction. I can now do refactorings in about
+> 1% of the keystrokes that it would have taken me previously when we had no way for
+> code to format itself.
-## Testimonials
+**Dusty Phillips**,
+[writer](https://smile.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dusty+phillips):
-**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.
-> Black is opinionated so you don't have to be.
-
-**Hynek Schlawack**, [creator of `attrs`](http://www.attrs.org/), core
-developer of Twisted and CPython:
+**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!
@@ -354,171 +165,66 @@ developer of Twisted and CPython:
> At least the name is good.
-**Kenneth Reitz**, creator of [`requests`](http://python-requests.org/)
-and [`pipenv`](https://docs.pipenv.org/):
+**Kenneth Reitz**, creator of [`requests`](http://python-requests.org/) and
+[`pipenv`](https://readthedocs.org/projects/pipenv/):
> This vastly improves the formatting of our code. Thanks a ton!
-
## Show your style
Use the badge in your project's README.md:
-```markdown
-[](https://github.com/ambv/black)
+```md
+[](https://github.com/psf/black)
```
-Looks like this: [](https://github.com/ambv/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:
+[](https://github.com/psf/black)
## License
MIT
+## Contributing
-## Contributing to Black
+Welcome! Happy to see you willing to make the project better. You can get started by
+reading this:
-In terms of inspiration, *Black* is about as configurable as *gofmt* and
-*rustfmt* are. This is deliberate.
+- [Contributing: The basics](https://black.readthedocs.io/en/latest/contributing/the_basics.html)
-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.
+You can also take a look at the rest of the contributing docs or talk with the
+developers:
-More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
+- [Contributing documentation](https://black.readthedocs.io/en/latest/contributing/index.html)
+- [Chat on Discord](https://discord.gg/RtVdv86PrH)
+## Change log
-## Change Log
+The log has become rather long. It moved to its own file.
-### 18.3a5 (unreleased)
+See [CHANGES](https://black.readthedocs.io/en/latest/change_log.html).
-* added `--diff` (#87)
-
-* add line breaks before all delimiters, except in cases like commas, to better
- comply with PEP 8 (#73)
-
-* 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)
-
-* fixed 18.3a4 regression: don't crash and burn on empty lines with
- trailing whitespace (#80)
-
-* when CTRL+C is pressed while formatting many files, Black no longer
- freaks out with a flurry of asyncio-related exceptions
-
-* only allow up to two empty lines on module level and only single empty
- lines within functions (#74)
-
-
-### 18.3a4
-
-* `# fmt: off` and `# fmt: on` are implemented (#5)
-
-* automatic detection of deprecated Python 2 forms of print statements
- and exec statements in the formatted file (#49)
-
-* use proper spaces for complex expressions in default values of typed
- function arguments (#60)
-
-* only return exit code 1 when --check is used (#50)
-
-* don't remove single trailing commas from square bracket indexing
- (#59)
-
-* don't omit whitespace if the previous factor leaf wasn't a math
- operator (#55)
-
-* omit extra space in kwarg unpacking if it's the first argument (#46)
-
-* omit extra space in [Sphinx auto-attribute comments](http://www.sphinx-doc.org/en/stable/ext/autodoc.html#directive-autoattribute)
- (#68)
-
-
-### 18.3a3
-
-* don't remove single empty lines outside of bracketed expressions
- (#19)
-
-* added ability to pipe formatting from stdin to stdin (#25)
-
-* restored ability to format code with legacy usage of `async` as
- a name (#20, #42)
-
-* even better handling of numpy-style array indexing (#33, again)
-
-
-### 18.3a2
-
-* 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)
-
-* ignore empty bracket pairs while splitting. This avoids very weirdly
- looking formattings (#34, #35)
-
-* remove a trailing comma if there is a single argument to a call
-
-* if top level functions were separated by a comment, don't put four
- empty lines after the upper function
-
-* fixed unstable formatting of newlines with imports
-
-* fixed unintentional folding of post scriptum standalone comments
- into last statement if it was a simple statement (#18, #28)
-
-* fixed missing space in numpy-style array indexing (#33)
-
-* fixed spurious space after star-based unary expressions (#31)
-
-
-### 18.3a1
-
-* added `--check`
-
-* 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)
-
-* fixed invalid spacing of dots in relative imports (#6, #13)
-
-* fixed invalid splitting after comma on unpacked variables in for-loops
- (#23)
-
-* fixed spurious space in parenthesized set expressions (#7)
-
-* fixed spurious space after opening parentheses and in default
- arguments (#14, #17)
-
-* fixed spurious space after unary operators when the operand was
- a complex expression (#15)
-
-
-### 18.3a0
-
-* first published version, Happy ð° Day 2018!
-
-* alpha quality
+## Authors
-* date-versioned (see: https://calver.org/)
+The author list is quite long nowadays, so it lives in its own file.
+See [AUTHORS.md](./AUTHORS.md)
-## Authors
+## Code of Conduct
-Glued together by [Åukasz Langa](mailto:lukasz@langa.pl).
+Everyone participating in the _Black_ project, and in particular in the issue tracker,
+pull requests, and social media activity, is expected to treat other people with respect
+and more generally to follow the guidelines articulated in the
+[Python Community Code of Conduct](https://www.python.org/psf/codeofconduct/).
-Maintained with [Carol Willing](mailto:carolcode@willingconsulting.com)
-and [Carl Meyer](mailto:carl@oddbird.net).
+At the same time, humor is encouraged. In fact, basic familiarity with Monty Python's
+Flying Circus is expected. We are not savages.
-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
-* [Mika Naylor](mailto:mail@autophagy.io)
-* [Osaetin Daniel](mailto:osaetindaniel@gmail.com)
+And if you _really_ need to slap somebody, do it with a fish while dancing.