*Black* is the uncompromising Python code formatter. By using it, you
-agree to cease control over minutiae of hand-formatting. In return,
+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.
possible.
-## NOTE: This is an early pre-release
+## Installation and Usage
-*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``.
-
-
-## Installation
+### 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* is able to parse all of the new syntax supported on Python 3.6
-but also *effectively all* the Python 2 syntax at the same time.
-## Usage
+### 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:
-l, --line-length INTEGER Where to wrap around. [default: 88]
- --check Don't write back the files, just return the
+ --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.
```
used).
-## The philosophy behind *Black*
+### 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
the same effect, as a courtesy for straddling code.
-### How *Black* formats files
+### 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.
+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,
debug: bool = False,
):
"""Applies `variables` to the `template` and writes to `file`."""
- with open(file, 'w') as f:
+ with open(file, "w") as f:
...
```
indentation level (like the arguments list and the docstring in the
example above).
-Unnecessary trailing commas are removed if an expression fits in one
-line. This makes it 1% more likely that your line won't exceed the
-allotted line length limit.
-
-*Black* avoids spurious vertical whitespace. This is in the spirit of
-PEP 8 which says that in-function vertical whitespace should only be
-used sparingly. One exception is control flow statements: *Black* will
-always emit an extra empty line after ``return``, ``raise``, ``break``,
-``continue``, and ``yield``. This is to make changes in control flow
-more prominent to readers of your code.
-
-That's it. The rest of the whitespace formatting rules follow PEP 8 and
-are designed to keep `pycodestyle` quiet.
+If a line of "from" imports cannot fit in the allotted length, it's always split
+into one per line. Imports tend to change often and this minimizes diffs, as well
+as enables readers of code to easily find which commit introduced a particular
+import. This exception also makes *Black* compatible with
+[isort](https://pypi.org/p/isort/). Use `multi_line_output=3` and
+`include_trailing_comma=True` in your isort config.
### Line length
### Empty lines
-*Black* will allow single empty lines left by the original editors,
-except when they're added within parenthesized expressions. Since such
-expressions are always reformatted to fit minimal space, this whitespace
-is lost.
+*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. *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.
+after module-level functions. *Black* will not put empty lines between
+function/class definitions and standalone comments that immediately precede
+the given function/class.
+
+
+### 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.
+
+### 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 (...)`
+
+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. Otherwise, the parentheses are always added.
+
+
+## Editor integration
+
+### Emacs
+
+Use [proofit404/blacken](https://github.com/proofit404/blacken).
+
+
+### PyCharm
+
+1. Install `black`.
+
+ $ pip install black
+
+2. Locate your `black` installation folder.
+
+ On MacOS / Linux / BSD:
+
+ $ which black
+ /usr/local/bin/black # possible location
+
+ On Windows:
+
+ $ where black
+ %LocalAppData%\Programs\Python\Python36-32\Scripts\black.exe # possible location
+3. Open External tools in PyCharm with `File -> Settings -> Tools -> External Tools`.
-### Editor integration
+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: <install_location_from_step_2>
+ - Arguments: $FilePath$
-* Visual Studio Code: [joslarson.black-vscode](https://marketplace.visualstudio.com/items?itemName=joslarson.black-vscode)
+5. Format the currently opened file by selecting `Tools -> External Tools -> black`.
+ - Alternatively, you can set a keyboard shortcut by navigating to `Preferences -> Keymap`.
+
+
+### 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 with [vim-plug](https://github.com/junegunn/vim-plug):
+
+```
+Plug 'ambv/black',
+```
+
+or with [Vundle](https://github.com/VundleVim/Vundle.vim):
+
+```
+Plugin 'ambv/black'
+```
+
+or you can copy the plugin from [plugin/black.vim](https://github.com/ambv/black/tree/master/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), just
+create a virtualenv manually and point `g:black_virtualenv` to it.
+The plugin will use it.
+
+**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.
+
+
+### Visual Studio Code
+
+Use [joslarson.black-vscode](https://marketplace.visualstudio.com/items?itemName=joslarson.black-vscode).
+
+### SublimeText 3
+
+Use [sublack plugin](https://github.com/jgirardet/sublack).
+
+### Other editors
+
+Atom/Nuclide integration is planned by the author, others will
+require external contributions.
+
+Patches welcome! ✨ 🍰 ✨
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)).
passed). *Black* will still emit messages on stderr but that shouldn't
affect your use case.
-There is currently no integration with any other text editors. Vim and
-Atom/Nuclide integration is planned by the author, others will require
-external contributions.
+This can be used for example with PyCharm's [File Watchers](https://www.jetbrains.com/help/pycharm/file-watchers.html).
-Patches welcome! ✨ 🍰 ✨
+
+## 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.
+
+`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.
+
+
+## Ignoring non-modified files
+
+*Black* remembers files it already formatted, unless the `--diff` flag is used or
+code is passed via standard input. This information is stored per-user. The exact
+location of the file depends on the black version and the system on which black
+is run. The file is non-portable. The standard location on common operating systems
+is:
+
+* Windows: `C:\\Users\<username>\AppData\Local\black\black\Cache\<version>\cache.<line-length>.pickle`
+* macOS: `/Users/<username>/Library/Caches/black/<version>/cache.<line-length>.pickle`
+* Linux: `/home/<username>/.cache/black/<version>/cache.<line-length>.pickle`
## Testimonials
MIT
-## Contributing
+## Contributing to Black
-In terms of inspiration, *Black* is about as configurable as *gofmt* and
-*rustfmt* are. This is deliberate.
+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
## Change Log
+### 18.4a4
+
+* don't populate the cache on `--check` (#175)
+
+
+### 18.4a3
+
+* added a "cache"; files already reformatted that haven't changed on disk
+ won't be reformatted again (#109)
+
+* `--check` and `--diff` are no longer mutually exclusive (#149)
+
+* generalized star expression handling, including double stars; this
+ fixes multiplication making expressions "unsafe" for trailing commas (#132)
+
+* Black no longer enforces putting empty lines behind control flow statements
+ (#90)
+
+* Black now splits imports like "Mode 3 + trailing comma" of isort (#127)
+
+* fixed comment indentation when a standalone comment closes a block (#16, #32)
+
+* fixed standalone comments receiving extra empty lines if immediately preceding
+ a class, def, or decorator (#56, #154)
+
+* fixed `--diff` not showing entire path (#130)
+
+* fixed parsing of complex expressions after star and double stars in
+ function calls (#2)
+
+* fixed invalid splitting on comma in lambda arguments (#133)
+
+* fixed missing splits of ternary expressions (#141)
+
+
+### 18.4a2
+
+* fixed parsing of unaligned standalone comments (#99, #112)
+
+* fixed placement of dictionary unpacking inside dictionary literals (#111)
+
+* Vim plugin now works on Windows, too
+
+* fixed unstable formatting when encountering unnecessarily escaped quotes
+ in a string (#120)
+
+
+### 18.4a1
+
+* added `--quiet` (#78)
+
+* added automatic parentheses management (#4)
+
+* added [pre-commit](https://pre-commit.com) integration (#103, #104)
+
+* fixed reporting on `--check` with multiple files (#101, #102)
+
+* fixed removing backslash escapes from raw strings (#100, #105)
+
+
+### 18.4a0
+
+* added `--diff` (#87)
+
+* add line breaks before all delimiters, except in cases like commas, to
+ better comply with PEP 8 (#73)
+
+* standardize string literals to use double quotes (almost) everywhere
+ (#75)
+
+* 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)
+
+* fixed 18.3a4 regression: `# yapf: disable` usage as trailing comment
+ would cause Black to not emit the rest of the file (#95)
+
+* 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)
## Authors
Glued together by [Łukasz Langa](mailto:lukasz@langa.pl).
+
+Maintained with [Carol Willing](mailto:carolcode@willingconsulting.com),
+[Carl Meyer](mailto:carl@oddbird.net),
+[Mika Naylor](mailto:mail@autophagy.io), and
+[Zsolt Dollenstein](mailto:zsol.zsol@gmail.com).
+
+Multiple contributions by:
+* [Anthony Sottile](mailto:asottile@umich.edu)
+* [Artem Malyshev](mailto:proofit404@gmail.com)
+* [Daniel M. Capella](mailto:polycitizen@gmail.com)
+* [Eli Treuherz](mailto:eli.treuherz@cgi.com)
+* Hugo van Kemenade
+* [Ivan Katanić](mailto:ivan.katanic@gmail.com)
+* [Jonas Obrist](mailto:ojiidotch@gmail.com)
+* [Osaetin Daniel](mailto:osaetindaniel@gmail.com)
+* [Vishwas B Sharma](mailto:sharma.vishwas88@gmail.com)
projects / etc / vim.git / blobdiff