X-Git-Url: https://git.madduck.net/etc/vim.git/blobdiff_plain/74f8c1316ce36bb551db709d1a85fa90254b94dd..0196437f8e062817d3277bb1484de3fbdcb3e19d:/README.md diff --git a/README.md b/README.md index dfbcc51..3c63cb5 100644 --- a/README.md +++ b/README.md @@ -1,140 +1,270 @@ -![Black Logo](https://raw.githubusercontent.com/ambv/black/master/docs/_static/logo2-readme.png) +![Black Logo](https://raw.githubusercontent.com/psf/black/master/docs/_static/logo2-readme.png) +

The Uncompromising Code Formatter

-Build Status -Documentation Status -Coverage Status -License: MIT -PyPI -Code style: black +Build Status +Actions Status +Actions Status +Documentation Status +Coverage Status +License: MIT +PyPI +Downloads +Code style: black

> “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* is the uncompromising Python code formatter. By using it, you -agree to cease control over minutiae of hand-formatting. In return, -*Black* gives you speed, determinism, and freedom from `pycodestyle` -nagging about formatting. You will save time and mental energy for -more important matters. +_Black_ makes code review faster by producing the smallest diffs possible. -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. +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. -*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)** | +**[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)** -## 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**. +## Installation and usage -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 +_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. -## Installation +### Usage -*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. +To get started right away with sensible defaults: +```sh +black {source_file_or_directory} +``` -## Usage +### Command line options +_Black_ doesn't provide many options. You can list them by running `black --help`: -``` -black [OPTIONS] [SRC]... +```text +Usage: black [OPTIONS] [SRC]... + + The uncompromising code formatter. Options: - -l, --line-length INTEGER Where to wrap around. [default: 88] - --check Don't write back the files, just return the - status. Return code 0 means nothing would - change. Return code 1 means some files would be - reformatted. Return code 123 means there was an - internal error. - --fast / --safe If --fast given, skip temporary sanity checks. - [default: --safe] - --version Show the version and exit. - --help Show this message and exit. -``` - -*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). - - -## The philosophy behind *Black* - -*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* formats files - -*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. - -As for vertical whitespace, *Black* tries to render one full expression -or simple statement per line. If this fits the allotted line length, -great. + -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] + + --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. + + --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: /(\.eggs|\.git|\.hg|\.mypy + _cache|\.nox|\.tox|\.venv|\.svn|_build|buck- + out|build|dist)/] + + --force-exclude TEXT Like --exclude, but files and directories + matching this regex will be excluded even + when they are passed explicitly as arguments + + -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 FILE 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). + +### Using _Black_ with other tools + +While _Black_ enforces formatting that conforms to PEP 8, other tools may raise warnings +about _Black_'s changes or will overwrite _Black_'s changes. A good example of this is +[isort](https://pypi.org/p/isort). Since _Black_ is barely configurable, these tools +should be configured to neither warn about nor overwrite _Black_'s changes. + +Actual details on _Black_ compatible configurations for various tools can be found in +[compatible_configs](https://github.com/psf/black/blob/master/docs/compatible_configs.md). + +### Migrating your code style without ruining git blame + +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. + +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. + +``` +# Migrate code style to Black +5b4ab991dede475d393e9d69ec388fd6bd949699 +``` + +Afterwards, you can pass that file to `git blame` and see clean and meaningful blame +information. + +```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 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 +``` + +**The one caveat is that GitHub and GitLab do not yet support ignoring revisions using +their native UI of blame.** So blame information will be cluttered with a reformatting +commit on those platforms. (If you'd like this feature, there's an open issue for +[GitLab](https://gitlab.com/gitlab-org/gitlab/-/issues/31423) and please let GitHub +know!) + +### NOTE: This is a beta product + +_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: -l = [1, +j = [1, 2, - 3, + 3 ] # out: -l = [1, 2, 3] +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. +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()]] +ImportantClass.important_method(exc, limit, lookup_lines, capture_locals, extra_argument) # out: -l = [ - [n for n in list_bosses()], [n for n in list_employees()] -] +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. +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): +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: ... @@ -145,254 +275,1167 @@ 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: + 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). +_Black_ prefers parentheses over backslashes, and will remove backslashes if found. + +```py3 +# in: + +if some_short_rule1 \ + and some_short_rule2: + ... + +# out: + +if some_short_rule1 and some_short_rule2: + ... + + +# in: + +if some_long_rule1 \ + and some_long_rule2: + ... + +# out: + +if ( + some_long_rule1 + and some_long_rule2 +): + ... + +``` + +Backslashes and multiline strings are one of the two places in the Python grammar that +break significant indentation. You never need backslashes, they are used to force the +grammar to accept breaks that would otherwise be parse errors. That makes them confusing +to look at and brittle to modify. This is why _Black_ always gets rid of them. + +If you're reaching for backslashes, that's a clear signal that you can do better if you +slightly refactor your code. I hope some of the examples above show you that there are +many ways in which you can do it. + +However there is one exception: `with` statements using multiple context managers. +Python's grammar does not allow organizing parentheses around the series of context +managers. + +We don't want formatting like: + +```py3 +with make_context_manager1() as cm1, make_context_manager2() as cm2, make_context_manager3() as cm3, make_context_manager4() as cm4: + ... # nothing to split on - line too long +``` + +So _Black_ will now format it like this: -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. +```py3 +with \ + make_context_manager(1) as cm1, \ + make_context_manager(2) as cm2, \ + make_context_manager(3) as cm3, \ + make_context_manager(4) as cm4 \ +: + ... # backslashes and an ugly stranded colon +``` -*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. +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). -That's it. The rest of the whitespace formatting rules follow PEP 8 and -are designed to keep `pycodestyle` quiet. +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: +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 +ignore = E203, E501, W503 ``` -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". +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* 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 +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 recommends no spaces around `:` operators for "simple expressions" +(`ham[lower:upper]`), and extra space for "complex expressions" +(`ham[lower : upper + offset]`). _Black_ treats anything more than variable names as +"complex" (`ham[lower : upper + 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: -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. +```py3 +return not (this or that) +decision = (maybe.this() and values > 0) or (maybe.that() and values < 0) +``` +### Call chains -### Editor integration +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: -* Visual Studio Code: [joslarson.black-vscode](https://marketplace.visualstudio.com/items?itemName=joslarson.black-vscode) +```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() + ) +``` -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. +### Typing stub files -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. +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). -Patches welcome! ✨ 🍰 ✨ +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. -## Testimonials +_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: -**Dusty Phillips**, [writer](https://smile.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dusty+phillips): +- 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]`. -> Black is opinionated so you don't have to be. +## Pragmatism -**Hynek Schlawack**, [creator of `attrs`](http://www.attrs.org/), core -developer of Twisted and CPython: +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. -> An auto-formatter that doesn't suck is all I want for Xmas! +### The magic trailing comma -**Carl Meyer**, [Django](https://www.djangoproject.com/) core developer: +_Black_ in general does not take existing formatting into account. -> At least the name is good. +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. -**Kenneth Reitz**, creator of [`requests`](http://python-requests.org/) -and [`pipenv`](https://docs.pipenv.org/): +For example: -> This vastly improves the formatting of our code. Thanks a ton! +```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` + +```toml +[tool.black] +line-length = 88 +target-version = ['py37'] +include = '\.pyi?$' +exclude = ''' + +( + /( + \.eggs # exclude a few common directories in the + | \.git # root of the project + | \.hg + | \.mypy_cache + | \.tox + | \.venv + | _build + | buck-out + | build + | dist + )/ + | foo.py # also separately exclude a file named foo.py in + # the root of the project +) +''' +``` -## Show your style +
-Use the badge in your project's README.md: +### Lookup hierarchy -```markdown -[![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/ambv/black) +Command-line options have defaults that you can see in `--help`. A `pyproject.toml` can +override those defaults. Finally, options provided by the user on the command line +override both. + +_Black_ will only ever use one `pyproject.toml` file during an entire run. It doesn't +look for multiple files, and doesn't compose configuration from different levels of the +file hierarchy. + +## Editor integration + +### Emacs + +Options include the following: + +- [purcell/reformatter.el](https://github.com/purcell/reformatter.el) +- [proofit404/blacken](https://github.com/proofit404/blacken) +- [Elpy](https://github.com/jorgenschaefer/elpy). + +### PyCharm/IntelliJ IDEA + +1. Install `black`. + +```console +$ pip install black ``` -Looks like this: [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/ambv/black) +2. Locate your `black` installation folder. +On macOS / Linux / BSD: -## License +```console +$ which black +/usr/local/bin/black # possible location +``` -MIT +On Windows: + +```console +$ where black +%LocalAppData%\Programs\Python\Python36-32\Scripts\black.exe # possible location +``` +Note that if you are using a virtual environment detected by PyCharm, this is an +unneeded step. In this case the path to `black` is `$PyInterpreterDirectory$/black`. -## Contributing +3. Open External tools in PyCharm/IntelliJ IDEA -In terms of inspiration, *Black* is about as configurable as *gofmt* and -*rustfmt* are. This is deliberate. +On macOS: -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. +`PyCharm -> Preferences -> Tools -> External Tools` -More details can be found in [CONTRIBUTING](CONTRIBUTING.md). +On Windows / Linux / BSD: +`File -> Settings -> Tools -> External Tools` -## Change Log +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 Watchers](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" in Advanced Options + +### 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. -### 18.3a4 +### Vim -* `# fmt: off` and `# fmt: on` are implemented (#5) +Commands and shortcuts: -* automatic detection of deprecated Python 2 forms of print statements - and exec statements in the formatted file (#49) +- `: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. -* use proper spaces for complex expressions in default values of typed - function arguments (#60) +Configuration: -* only return exit code 1 when --check is used (#50) +- `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`) -* don't remove single trailing commas from square bracket indexing - (#59) +To install with [vim-plug](https://github.com/junegunn/vim-plug): -* don't omit whitespace if the previous factor leaf wasn't a math - operator (#55) +``` +Plug 'psf/black', { 'branch': 'stable' } +``` + +or with [Vundle](https://github.com/VundleVim/Vundle.vim): + +``` +Plugin 'psf/black' +``` + +and execute the following in a terminal: + +```console +$ cd ~/.vim/bundle/black +$ git checkout origin/stable -b stable +``` + +or you can copy the plugin from +[plugin/black.vim](https://github.com/psf/black/blob/stable/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. + +**I get an import error when using _Black_ from a virtual environment**: If you get an +error message like this: + +```text +Traceback (most recent call last): + File "", line 63, in + File "/home/gui/.vim/black/lib/python3.7/site-packages/black.py", line 45, in + from typed_ast import ast3, ast27 + File "/home/gui/.vim/black/lib/python3.7/site-packages/typed_ast/ast3.py", line 40, in + from typed_ast import _ast3 +ImportError: /home/gui/.vim/black/lib/python3.7/site-packages/typed_ast/_ast3.cpython-37m-x86_64-linux-gnu.so: undefined symbool: PyExc_KeyboardInterrupt +``` + +Then you need to install `typed_ast` and `regex` directly from the source code. The +error happens because `pip` will download [Python wheels](https://pythonwheels.com/) if +they are available. Python wheels are a new standard of distributing Python packages and +packages that have Cython and extensions written in C are already compiled, so the +installation is much more faster. The problem here is that somehow the Python +environment inside Vim does not match with those already compiled C extensions and these +kind of errors are the result. Luckily there is an easy fix: installing the packages +from the source code. + +The two packages that cause the problem are: + +- [regex](https://pypi.org/project/regex/) +- [typed-ast](https://pypi.org/project/typed-ast/) + +Now remove those two packages: + +```console +$ pip uninstall regex typed-ast -y +``` + +And now you can install them with: + +```console +$ pip install --no-binary :all: regex typed-ast +``` + +The C extensions will be compiled and now Vim's Python environment will match. Note that +you need to have the GCC compiler and the Python development files installed (on +Ubuntu/Debian do `sudo apt-get install build-essential python3-dev`). + +If you later want to update _Black_, you should do it like this: + +```console +$ pip install -U black --no-binary regex,typed-ast +``` + +### 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. -* omit extra space in kwarg unpacking if it's the first argument (#46) +### Atom/Nuclide -* omit extra space in [Sphinx auto-attribute comments](http://www.sphinx-doc.org/en/stable/ext/autodoc.html#directive-autoattribute) - (#68) +Use [python-black](https://atom.io/packages/python-black). +### Kakoune -### 18.3a3 +Add the following hook to your kakrc, then run _Black_ with `:format`. -* don't remove single empty lines outside of bracketed expressions - (#19) +``` +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! ✨ 🍰 ✨ -* added ability to pipe formatting from stdin to stdin (#25) +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. -* restored ability to format code with legacy usage of `async` as - a name (#20, #42) +This can be used for example with PyCharm's or IntelliJ's +[File Watchers](https://www.jetbrains.com/help/pycharm/file-watchers.html). -* even better handling of numpy-style array indexing (#33, again) +## 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. -### 18.3a2 +### Usage -* 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) +`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. -* ignore empty bracket pairs while splitting. This avoids very weirdly - looking formattings (#34, #35) +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. -* remove a trailing comma if there is a single argument to a call +`blackd` provides even less options than _Black_. You can see them by running +`blackd --help`: -* if top level functions were separated by a comment, don't put four - empty lines after the upper function +```text +Usage: blackd [OPTIONS] -* fixed unstable formatting of newlines with imports +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`: + +```sh +blackd --bind-port 9090 & # or let blackd choose a port +curl -s -XPOST "localhost:9090" -d "print('valid')" +``` + +### Protocol -* fixed unintentional folding of post scriptum standalone comments - into last statement if it was a simple statement (#18, #28) +`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`. -* fixed missing space in numpy-style array indexing (#33) +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). -* fixed spurious space after star-based unary expressions (#31) +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. -### 18.3a1 +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. -* added `--check` +Apart from the above, `blackd` can produce the following response codes: -* 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) +- `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. -* fixed invalid spacing of dots in relative imports (#6, #13) +The response headers include a `X-Black-Version` header containing the version of +_Black_. -* fixed invalid splitting after comma on unpacked variables in for-loops - (#23) +## black-primer -* fixed spurious space in parenthesized set expressions (#7) +`black-primer` is a tool built for CI (and huumans) to have _Black_ `--check` a number +of (configured in `primer.json`) Git accessible projects in parallel. _(A PR will be +accepted to add Mercurial support.)_ -* fixed spurious space after opening parentheses and in default - arguments (#14, #17) +### Run flow -* fixed spurious space after unary operators when the operand was - a complex expression (#15) +- Ensure we have a `black` + `git` in PATH +- Load projects from `primer.json` +- Run projects in parallel with `--worker` workers (defaults to CPU count / 2) + - Checkout projects + - Run black and record result + - Clean up repository checkout _(can optionally be disabled via `--keep`)_ +- Display results summary to screen +- Default to cleaning up `--work-dir` (which defaults to tempfile schemantics) +- Return + - 0 for successful run + - < 0 for environment / internal error + - > 0 for each project with an error +### Speed up Runs 🏎 -### 18.3a0 +If you're running locally yourself to test black on lots of code try: -* first published version, Happy 🍰 Day 2018! +- Using `-k` / `--keep` + `-w` / `--work-dir` so you don't have to re-checkout the repo + each run -* alpha quality +### CLI Arguments -* date-versioned (see: https://calver.org/) +```text +Usage: black-primer [OPTIONS] + primer - prime projects for blackening... 🏴 + +Options: + -c, --config PATH JSON config file path [default: /Users/cooper/repos/ + black/src/black_primer/primer.json] + + --debug Turn on debug logging [default: False] + -k, --keep Keep workdir + repos post run [default: False] + -L, --long-checkouts Pull big projects to test [default: False] + -R, --rebase Rebase project if already checked out [default: + False] + + -w, --workdir PATH Directory Path for repo checkouts [default: /var/fol + ders/tc/hbwxh76j1hn6gqjd2n2sjn4j9k1glp/T/primer.20200 + 517125229] + + -W, --workers INTEGER Number of parallel worker coroutines [default: 69] + -h, --help Show this message and exit. +``` + +### primer config file + +The config is JSON format. Its main element is the `"projects"` dictionary. Below +explains each parameter: + +```json +{ + "projects": { + "00_Example": { + "cli_arguments": "List of extra CLI arguments to pass Black for this project", + "expect_formatting_changes": "Boolean to indicate that the version of Black is expected to cause changes", + "git_clone_url": "URL you would pass `git clone` to check out this repo", + "long_checkout": "Boolean to have repo skipped by defauult unless `--long-checkouts` is specified", + "py_versions": "List of major Python versions to run this project with - all will do as you'd expect - run on ALL versions" + }, + "aioexabgp": { + "cli_arguments": [], + "expect_formatting_changes": true, + "git_clone_url": "https://github.com/cooperlees/aioexabgp.git", + "long_checkout": false, + "py_versions": ["all", "3.8"] // "all" ignores all other versions + } + } +} +``` + +### Example run + +```console +cooper-mbp:black cooper$ ~/venvs/b/bin/black-primer +[2020-05-17 13:06:40,830] INFO: 4 projects to run Black over (lib.py:270) +[2020-05-17 13:06:44,215] INFO: Analyzing results (lib.py:285) +-- primer results 📊 -- + +3 / 4 succeeded (75.0%) ✅ +1 / 4 FAILED (25.0%) 💩 + - 0 projects disabled by config + - 0 projects skipped due to Python version + - 0 skipped due to long checkout + +Failed projects: + +### flake8-bugbear: + - Returned 1 + - stdout: +--- tests/b303_b304.py 2020-05-17 20:04:09.991227 +0000 ++++ tests/b303_b304.py 2020-05-17 20:06:42.753851 +0000 +@@ -26,11 +26,11 @@ + maxint = 5 # this is okay + # the following shouldn't crash + (a, b, c) = list(range(3)) + # it's different than this + a, b, c = list(range(3)) +- a, b, c, = list(range(3)) ++ a, b, c = list(range(3)) + # and different than this + (a, b), c = list(range(3)) + a, *b, c = [1, 2, 3, 4, 5] + b[1:3] = [0, 0] + +would reformat tests/b303_b304.py +Oh no! 💥 💔 💥 +1 file would be reformatted, 22 files would be left unchanged. +``` + +## 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 branch that tracks 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, Bandersnatch, Pipenv, virtualenv), pandas, Pillow, +every Datadog Agent Integration, Home Assistant. + +The following organizations use _Black_: Facebook, Dropbox. + +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](https://github.com/psf/black/blob/master/CONTRIBUTING.md). + +## Change Log + +The log's become rather long. It moved to its own file. + +See [CHANGES](https://github.com/psf/black/blob/master/CHANGES.md). ## Authors Glued together by [Łukasz Langa](mailto:lukasz@langa.pl). + +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)