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+
The Uncompromising Code Formatter
-
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-
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-
-
+
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+
+
+
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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.
-*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.
-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* makes code review faster by producing the smallest diffs
-possible.
+Try it out now using the [Black Playground](https://black.now.sh). Watch the
+[PyCon 2019 talk](https://youtu.be/esZLCuWs_2Y) to learn more.
+---
-## Installation and Usage
+_Contents:_ **[Installation and usage](#installation-and-usage)** |
+**[Code style](#the-black-code-style)** | **[Pragmatism](#pragmatism)** |
+**[pyproject.toml](#pyprojecttoml)** | **[Editor integration](#editor-integration)** |
+**[blackd](#blackd)** | **[Version control integration](#version-control-integration)**
+| **[Ignoring unmodified files](#ignoring-unmodified-files)** | **[Used by](#used-by)**
+| **[Testimonials](#testimonials)** | **[Show your style](#show-your-style)** |
+**[Contributing](#contributing-to-black)** | **[Change Log](#change-log)** |
+**[Authors](#authors)**
-### Installation
+---
+
+## Installation and 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.
+### Installation
+_Black_ can be installed by running `pip install black`. It requires Python 3.6.0+ to
+run but you can reformat Python 2 code with it, too.
### Usage
@@ -45,112 +58,148 @@ black {source_file_or_directory}
### Command line options
-Black doesn't provide many options. You can list them by running
-`black --help`:
+_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]
- -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.
-```
-
-*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 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.
+ -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.
+ --fast / --safe If --fast given, skip temporary sanity
+ checks. [default: --safe]
+ --include TEXT A regular expression that matches files and
+ directories that should be included on
+ recursive searches. An empty value means
+ all files are included regardless of the
+ name. Use forward slashes for directories
+ on all platforms (Windows, too). Exclusions
+ are calculated first, inclusions later.
+ [default: \.pyi?$]
+ --exclude TEXT A regular expression that matches files and
+ directories that should be excluded on
+ recursive searches. An empty value means no
+ paths are excluded. Use forward slashes for
+ directories on all platforms (Windows, too).
+ Exclusions are calculated first, inclusions
+ later. [default: /(\.eggs|\.git|\.hg|\.mypy
+ _cache|\.nox|\.tox|\.venv|_build|buck-
+ out|build|dist)/]
+ -q, --quiet Don't emit non-error messages to stderr.
+ Errors are still emitted, silence those with
+ 2>/dev/null.
+ -v, --verbose Also emit messages to stderr about files
+ that were not changed or were ignored due to
+ --exclude=.
+ --version Show the version and exit.
+ --config PATH Read configuration from PATH.
+ -h, --help Show this message and exit.
+```
+
+_Black_ is a well-behaved Unix-style command-line tool:
+
+- it does nothing if no sources are passed to it;
+- it will read from standard input and write to standard output if `-` is used as the
+ filename;
+- it only outputs messages to users on standard error;
+- exits with code 0 unless an internal error occurred (or `--check` was used).
+
+### 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](./docs/compatible_configs.md).
+
+### 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:
...
@@ -161,6 +210,8 @@ 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`."""
@@ -168,159 +219,198 @@ def very_important_function(
...
```
-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).
+You might have noticed that closing brackets are always dedented and that a trailing
+comma is always added. Such formatting produces smaller diffs; when you add or remove an
+element, it's always just one line. Also, having the closing bracket dedented provides a
+clear delimiter between two distinct sections of the code that otherwise share the same
+indentation level (like the arguments list and the docstring in the example above).
+
+If a data structure literal (tuple, list, set, dict) or a line of "from" imports cannot
+fit in the allotted length, it's always split into one element per line. This minimizes
+diffs as well as enables readers of code to find which commit introduced a particular
+entry. This also makes _Black_ compatible with [isort](https://pypi.org/p/isort/) with
+the following configuration.
+
+
+A compatible `.isort.cfg`
-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`,
-`include_trailing_comma=True`, `force_grid_wrap=0`, and `line_length=88` in your
-isort config.
+```
+[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* 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_ 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.
-*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.
-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 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.
+_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)
+_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.
+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.
+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.
+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:
+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 (...):`
@@ -333,418 +423,641 @@ interesting cases:
- `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. Otherwise, the parentheses are always added.
-
+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.
-## Editor integration
-
-### Emacs
+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:
-Use [proofit404/blacken](https://github.com/proofit404/blacken).
-
-
-### PyCharm
-
-1. Install `black`.
+```py3
+return not (this or that)
+decision = (maybe.this() and values > 0) or (maybe.that() and values < 0)
+```
- $ pip install black
+### Call chains
-2. Locate your `black` installation folder.
+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:
- On MacOS / Linux / BSD:
+```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()
+ )
+```
- $ which black
- /usr/local/bin/black # possible location
+### Typing stub files
- On Windows:
+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).
- $ where black
- %LocalAppData%\Programs\Python\Python36-32\Scripts\black.exe # possible location
+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:
-3. Open External tools in PyCharm with `File -> Settings -> Tools -> External Tools`.
+- 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.
-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: $FilePath$
+_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:
-5. Format the currently opened file by selecting `Tools -> External Tools -> black`.
- - Alternatively, you can set a keyboard shortcut by navigating to `Preferences -> Keymap`.
+- all function bodies should be empty (contain `...` instead of the body);
+- do not use docstrings;
+- prefer `...` over `pass`;
+- for arguments with a default, use `...` instead of the actual default;
+- avoid using string literals in type annotations, stub files support forward references
+ natively (like Python 3.7 code with `from __future__ import annotations`);
+- use variable annotations instead of type comments, even for stubs that target older
+ versions of Python;
+- for arguments that default to `None`, use `Optional[]` explicitly;
+- use `float` instead of `Union[int, float]`.
+## Pragmatism
-### Vim
+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.
-Commands and shortcuts:
+### The magic trailing comma
-* `,=` 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_ in general does not take existing formatting into account.
-Configuration:
-* `g:black_fast` (defaults to `0`)
-* `g:black_linelength` (defaults to `88`)
-* `g:black_virtualenv` (defaults to `~/.vim/black`)
+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.
-To install with [vim-plug](https://github.com/junegunn/vim-plug):
+For example:
+```py3
+TRANSLATIONS = {
+ "en_us": "English (US)",
+ "pl_pl": "polski",
+}
```
-Plug 'ambv/black',
-```
-
-or with [Vundle](https://github.com/VundleVim/Vundle.vim):
+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
+)
+'''
```
-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.
+### Lookup hierarchy
-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.
+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.
-**How to get Vim with Python 3.6?**
-On Ubuntu 17.10 Vim comes with Python 3.6 by default.
-On macOS with HomeBrew run: `brew install vim --with-python3`.
-When building Vim from source, use:
-`./configure --enable-python3interp=yes`. There's many guides online how
-to do this.
+_Black_ 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
-### 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
+### Emacs
-Atom/Nuclide integration is planned by the author, others will
-require external contributions.
+Use [proofit404/blacken](https://github.com/proofit404/blacken) or
+[Elpy](https://github.com/jorgenschaefer/elpy).
-Patches welcome! ⨠ð° â¨
+### PyCharm/IntelliJ IDEA
-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.
+1. Install `black`.
-This can be used for example with PyCharm's [File Watchers](https://www.jetbrains.com/help/pycharm/file-watchers.html).
+```console
+$ pip install black
+```
+2. Locate your `black` installation folder.
-## Version control integration
+On macOS / Linux / BSD:
-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
+```console
+$ which black
+/usr/local/bin/black # possible location
```
-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.
+On Windows:
+```console
+$ where black
+%LocalAppData%\Programs\Python\Python36-32\Scripts\black.exe # possible location
+```
-## Ignoring non-modified files
+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`.
-*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:
+3. Open External tools in PyCharm/IntelliJ IDEA
-* Windows: `C:\\Users\\AppData\Local\black\black\Cache\\cache..pickle`
-* macOS: `/Users//Library/Caches/black//cache..pickle`
-* Linux: `/home//.cache/black//cache..pickle`
+On macOS:
+`PyCharm -> Preferences -> Tools -> External Tools`
-## Testimonials
+On Windows / Linux / BSD:
-**Dusty Phillips**, [writer](https://smile.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dusty+phillips):
+`File -> Settings -> Tools -> External Tools`
-> Black is opinionated so you don't have to be.
+4. Click the + icon to add a new external tool with the following values:
-**Hynek Schlawack**, [creator of `attrs`](http://www.attrs.org/), core
-developer of Twisted and CPython:
+ - Name: Black
+ - Description: Black is the uncompromising Python code formatter.
+ - Program:
+ - Arguments: `"$FilePath$"`
-> An auto-formatter that doesn't suck is all I want for Xmas!
+5. Format the currently opened file by selecting `Tools -> External Tools -> black`.
-**Carl Meyer**, [Django](https://www.djangoproject.com/) core developer:
+ - Alternatively, you can set a keyboard shortcut by navigating to
+ `Preferences or Settings -> Keymap -> External Tools -> External Tools - Black`.
-> At least the name is good.
+6. Optionally, run _Black_ on every file save:
-**Kenneth Reitz**, creator of [`requests`](http://python-requests.org/)
-and [`pipenv`](https://docs.pipenv.org/):
+ 1. Make sure you have the
+ [File Watcher](https://plugins.jetbrains.com/plugin/7177-file-watchers) plugin
+ installed.
+ 2. Go to `Preferences or Settings -> Tools -> File Watchers` and click `+` to add a
+ new watcher:
+ - Name: Black
+ - File type: Python
+ - Scope: Project Files
+ - Program:
+ - Arguments: `$FilePath$`
+ - Output paths to refresh: `$FilePath$`
+ - Working directory: `$ProjectFileDir$`
-> This vastly improves the formatting of our code. Thanks a ton!
+ - Uncheck "Auto-save edited files to trigger the watcher"
+### Wing IDE
-## Show your style
+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:
-Use the badge in your project's README.md:
+1. Install `black`.
-```markdown
-[](https://github.com/ambv/black)
+```console
+$ pip install black
```
-Looks like this: [](https://github.com/ambv/black)
-
-
-## License
-
-MIT
+2. Make sure it runs from the command line, e.g.
+```console
+$ black --help
+```
-## Contributing to Black
+3. In Wing IDE, activate the **OS Commands** panel and define the command **black** to
+ execute black on the currently selected file:
-In terms of inspiration, *Black* is about as configurable as *gofmt*.
-This is deliberate.
+- 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
-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.
+4. Select a file in the editor and press **F1** , or whatever key binding you selected
+ in step 3, to reformat the file.
-More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
+### Vim
+Commands and shortcuts:
-## Change Log
+- `: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.
-### 18.5a0 (unreleased)
+Configuration:
-* slices are now formatted according to PEP 8 (#178)
+- `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`)
-* parentheses are now also managed automatically on the right-hand side
- of assignments and return statements (#140)
+To install with [vim-plug](https://github.com/junegunn/vim-plug):
-* math operators now use their respective priorities for delimiting multiline
- expressions (#148)
+```
+Plug 'psf/black', { 'branch': 'stable' }
+```
-* empty parentheses in a class definition are now removed (#145, #180)
+or with [Vundle](https://github.com/VundleVim/Vundle.vim):
-* fixed an invalid trailing comma sometimes left in imports (#185)
+```
+Plugin 'psf/black'
+```
-* fixed non-deterministic formatting when multiple pairs of removable parentheses
- were used (#183)
+and execute the following in a terminal:
-* fixed not splitting long from-imports with only a single name
+```console
+$ cd ~/.vim/bundle/black
+$ git checkout origin/stable -b stable
+```
-* fixed Python 3.6+ file discovery by also looking at function calls with
- unpacking. This fixed non-deterministic formatting if trailing commas
- where used both in function signatures with stars and function calls
- with stars but the former would be reformatted to a single line.
+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
+```
-### 18.4a4
+Let me know if this requires any changes to work with Vim 8's builtin `packadd`, or
+Pathogen, and so on.
-* don't populate the cache on `--check` (#175)
+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.
-### 18.4a3
+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.
-* added a "cache"; files already reformatted that haven't changed on disk
- won't be reformatted again (#109)
+To run _Black_ on save, add the following line to `.vimrc` or `init.vim`:
-* `--check` and `--diff` are no longer mutually exclusive (#149)
+```
+autocmd BufWritePre *.py execute ':Black'
+```
-* generalized star expression handling, including double stars; this
- fixes multiplication making expressions "unsafe" for trailing commas (#132)
+To run _Black_ on a key press (e.g. F9 below), add this:
-* Black no longer enforces putting empty lines behind control flow statements
- (#90)
+```
+nnoremap :Black
+```
-* Black now splits imports like "Mode 3 + trailing comma" of isort (#127)
+**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.
-* fixed comment indentation when a standalone comment closes a block (#16, #32)
+### Visual Studio Code
-* fixed standalone comments receiving extra empty lines if immediately preceding
- a class, def, or decorator (#56, #154)
+Use the
+[Python extension](https://marketplace.visualstudio.com/items?itemName=ms-python.python)
+([instructions](https://code.visualstudio.com/docs/python/editing#_formatting)).
-* fixed `--diff` not showing entire path (#130)
+### SublimeText 3
-* fixed parsing of complex expressions after star and double stars in
- function calls (#2)
+Use [sublack plugin](https://github.com/jgirardet/sublack).
-* fixed invalid splitting on comma in lambda arguments (#133)
+### Jupyter Notebook Magic
-* fixed missing splits of ternary expressions (#141)
+Use [blackcellmagic](https://github.com/csurfer/blackcellmagic).
+### Python Language Server
-### 18.4a2
+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.
-* fixed parsing of unaligned standalone comments (#99, #112)
+### Atom/Nuclide
-* fixed placement of dictionary unpacking inside dictionary literals (#111)
+Use [python-black](https://atom.io/packages/python-black).
-* Vim plugin now works on Windows, too
+### Kakoune
-* fixed unstable formatting when encountering unnecessarily escaped quotes
- in a string (#120)
+Add the following hook to your kakrc, then run black with `:format`.
+```
+hook global WinSetOption filetype=python %{
+ set-option window formatcmd 'black -q -'
+}
+```
-### 18.4a1
+### Thonny
-* added `--quiet` (#78)
+Use [Thonny-black-code-format](https://github.com/Franccisco/thonny-black-code-format).
-* added automatic parentheses management (#4)
+### Other editors
-* added [pre-commit](https://pre-commit.com) integration (#103, #104)
+Other editors will require external contributions.
-* fixed reporting on `--check` with multiple files (#101, #102)
+Patches welcome! ⨠ð° â¨
-* fixed removing backslash escapes from raw strings (#100, #105)
+Any tool that can pipe code through _Black_ using its stdio mode (just
+[use `-` as the file name](https://www.tldp.org/LDP/abs/html/special-chars.html#DASHREF2)).
+The formatted code will be returned on stdout (unless `--check` was passed). _Black_
+will still emit messages on stderr but that shouldn't affect your use case.
+This can be used for example with PyCharm's or IntelliJ's
+[File Watchers](https://www.jetbrains.com/help/pycharm/file-watchers.html).
-### 18.4a0
+## blackd
-* added `--diff` (#87)
+`blackd` is a small HTTP server that exposes _Black_'s functionality over a simple
+protocol. The main benefit of using it is to avoid paying the cost of starting up a new
+_Black_ process every time you want to blacken a file.
-* add line breaks before all delimiters, except in cases like commas, to
- better comply with PEP 8 (#73)
+### Usage
-* standardize string literals to use double quotes (almost) everywhere
- (#75)
+`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.
-* 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)
+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.
-* fixed 18.3a4 regression: don't crash and burn on empty lines with
- trailing whitespace (#80)
+`blackd` provides even less options than _Black_. You can see them by running
+`blackd --help`:
-* fixed 18.3a4 regression: `# yapf: disable` usage as trailing comment
- would cause Black to not emit the rest of the file (#95)
+```text
+Usage: blackd [OPTIONS]
-* when CTRL+C is pressed while formatting many files, Black no longer
- freaks out with a flurry of asyncio-related exceptions
+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.
+```
-* only allow up to two empty lines on module level and only single empty
- lines within functions (#74)
+There is no official blackd client tool (yet!). You can test that blackd is working
+using `curl`:
+```
+blackd --bind-port 9090 & # or let blackd choose a port
+curl -s -XPOST "localhost:9090" -d "print('valid')"
+```
-### 18.3a4
+### Protocol
+
+`blackd` only accepts `POST` requests at the `/` path. The body of the request should
+contain the python source code to be formatted, encoded according to the `charset` field
+in the `Content-Type` request header. If no `charset` is specified, `blackd` assumes
+`UTF-8`.
+
+There are a few HTTP headers that control how the source is formatted. These correspond
+to command line flags for _Black_. There is one exception to this: `X-Protocol-Version`
+which if present, should have the value `1`, otherwise the request is rejected with
+`HTTP 501` (Not Implemented).
+
+The headers controlling how code is formatted are:
+
+- `X-Line-Length`: corresponds to the `--line-length` command line flag.
+- `X-Skip-String-Normalization`: corresponds to the `--skip-string-normalization`
+ command line flag. If present and its value is not the empty string, no string
+ normalization will be performed.
+- `X-Fast-Or-Safe`: if set to `fast`, `blackd` will act as _Black_ does when passed the
+ `--fast` command line flag.
+- `X-Python-Variant`: if set to `pyi`, `blackd` will act as _Black_ does when passed the
+ `--pyi` command line flag. Otherwise, its value must correspond to a Python version or
+ a set of comma-separated Python versions, optionally prefixed with `py`. For example,
+ to request code that is compatible with Python 3.5 and 3.6, set the header to
+ `py3.5,py3.6`.
+- `X-Diff`: corresponds to the `--diff` command line flag. If present, a diff of the
+ formats will be output.
+
+If any of these headers are set to invalid values, `blackd` returns a `HTTP 400` error
+response, mentioning the name of the problematic header in the message body.
+
+Apart from the above, `blackd` can produce the following response codes:
+
+- `HTTP 204`: If the input is already well-formatted. The response body is empty.
+- `HTTP 200`: If formatting was needed on the input. The response body contains the
+ blackened Python code, and the `Content-Type` header is set accordingly.
+- `HTTP 400`: If the input contains a syntax error. Details of the error are returned in
+ the response body.
+- `HTTP 500`: If there was any kind of error while trying to format the input. The
+ response body contains a textual representation of the error.
+
+The response headers include a `X-Black-Version` header containing the version of
+_Black_.
-* `# fmt: off` and `# fmt: on` are implemented (#5)
+## Version control integration
-* automatic detection of deprecated Python 2 forms of print statements
- and exec statements in the formatted file (#49)
+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:
-* use proper spaces for complex expressions in default values of typed
- function arguments (#60)
+```yaml
+repos:
+ - repo: https://github.com/psf/black
+ rev: stable
+ hooks:
+ - id: black
+ language_version: python3.6
+```
-* only return exit code 1 when --check is used (#50)
+Then run `pre-commit install` and you're ready to go.
-* don't remove single trailing commas from square bracket indexing
- (#59)
+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.
-* don't omit whitespace if the previous factor leaf wasn't a math
- operator (#55)
+If you're already using Python 3.7, switch the `language_version` accordingly. Finally,
+`stable` is a tag that is pinned to the latest release on PyPI. If you'd rather run on
+master, this is also an option.
-* omit extra space in kwarg unpacking if it's the first argument (#46)
+## Ignoring unmodified files
-* omit extra space in [Sphinx auto-attribute comments](http://www.sphinx-doc.org/en/stable/ext/autodoc.html#directive-autoattribute)
- (#68)
+_Black_ remembers files it has already formatted, unless the `--diff` flag is used or
+code is passed via standard input. This information is stored per-user. The exact
+location of the file depends on the _Black_ version and the system on which _Black_ is
+run. The file is non-portable. The standard location on common operating systems is:
+- Windows:
+ `C:\\Users\\AppData\Local\black\black\Cache\\cache...pickle`
+- macOS:
+ `/Users//Library/Caches/black//cache...pickle`
+- Linux:
+ `/home//.cache/black//cache...pickle`
-### 18.3a3
+`file-mode` is an int flag that determines whether the file was formatted as 3.6+ only,
+as .pyi, and whether string normalization was omitted.
-* don't remove single empty lines outside of bracketed expressions
- (#19)
+To override the location of these files on macOS or Linux, set the environment variable
+`XDG_CACHE_HOME` to your preferred location. For example, if you want to put the cache
+in the directory you're running _Black_ from, set `XDG_CACHE_HOME=.cache`. _Black_ will
+then write the above files to `.cache/black//`.
-* added ability to pipe formatting from stdin to stdin (#25)
+## Used by
-* restored ability to format code with legacy usage of `async` as
- a name (#20, #42)
+The following notable open-source projects trust _Black_ with enforcing a consistent
+code style: pytest, tox, Pyramid, Django Channels, Hypothesis, attrs, SQLAlchemy,
+Poetry, PyPA applications (Warehouse, Pipenv, virtualenv), pandas, Pillow, every Datadog
+Agent Integration, Home Assistant.
-* even better handling of numpy-style array indexing (#33, again)
+The following organizations use _Black_: Dropbox.
+Are we missing anyone? Let us know.
-### 18.3a2
+## Testimonials
-* changed positioning of binary operators to occur at beginning of lines
- instead of at the end, following [a recent change to PEP8](https://github.com/python/peps/commit/c59c4376ad233a62ca4b3a6060c81368bd21e85b)
- (#21)
+**Dusty Phillips**,
+[writer](https://smile.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dusty+phillips):
-* ignore empty bracket pairs while splitting. This avoids very weirdly
- looking formattings (#34, #35)
+> _Black_ is opinionated so you don't have to be.
-* remove a trailing comma if there is a single argument to a call
+**Hynek Schlawack**, [creator of `attrs`](https://www.attrs.org/), core developer of
+Twisted and CPython:
-* if top level functions were separated by a comment, don't put four
- empty lines after the upper function
+> An auto-formatter that doesn't suck is all I want for Xmas!
-* fixed unstable formatting of newlines with imports
+**Carl Meyer**, [Django](https://www.djangoproject.com/) core developer:
-* fixed unintentional folding of post scriptum standalone comments
- into last statement if it was a simple statement (#18, #28)
+> At least the name is good.
-* fixed missing space in numpy-style array indexing (#33)
+**Kenneth Reitz**, creator of [`requests`](http://python-requests.org/) and
+[`pipenv`](https://docs.pipenv.org/):
-* fixed spurious space after star-based unary expressions (#31)
+> This vastly improves the formatting of our code. Thanks a ton!
+## Show your style
-### 18.3a1
+Use the badge in your project's README.md:
-* added `--check`
+```markdown
+[](https://github.com/psf/black)
+```
-* only put trailing commas in function signatures and calls if it's
- safe to do so. If the file is Python 3.6+ it's always safe, otherwise
- only safe if there are no `*args` or `**kwargs` used in the signature
- or call. (#8)
+Using the badge in README.rst:
-* fixed invalid spacing of dots in relative imports (#6, #13)
+```
+.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
+ :target: https://github.com/psf/black
+```
-* fixed invalid splitting after comma on unpacked variables in for-loops
- (#23)
+Looks like this:
+[](https://github.com/psf/black)
-* fixed spurious space in parenthesized set expressions (#7)
+## License
-* fixed spurious space after opening parentheses and in default
- arguments (#14, #17)
+MIT
-* fixed spurious space after unary operators when the operand was
- a complex expression (#15)
+## Contributing to _Black_
+In terms of inspiration, _Black_ is about as configurable as _gofmt_. This is
+deliberate.
-### 18.3a0
+Bug reports and fixes are always welcome! However, before you suggest a new feature or
+configuration knob, ask yourself why you want it. If it enables better integration with
+some workflow, fixes an inconsistency, speeds things up, and so on - go for it! On the
+other hand, if your answer is "because I don't like a particular formatting" then you're
+not ready to embrace _Black_ yet. Such changes are unlikely to get accepted. You can
+still try but prepare to be disappointed.
-* first published version, Happy ð° Day 2018!
+More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
-* alpha quality
+## Change Log
-* date-versioned (see: https://calver.org/)
+The log's become rather long. It moved to its own file.
+See [CHANGES](CHANGES.md).
## Authors
@@ -752,18 +1065,75 @@ Glued together by [Åukasz 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).
+[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:
-* [Anthony Sottile](mailto:asottile@umich.edu)
-* [Artem Malyshev](mailto:proofit404@gmail.com)
-* [Christian Heimes](mailto:christian@python.org)
-* [Daniel M. Capella](mailto:polycitizen@gmail.com)
-* [Eli Treuherz](mailto:eli.treuherz@cgi.com)
-* Hugo van Kemenade
-* [Ivan KataniÄ](mailto:ivan.katanic@gmail.com)
-* [Jonas Obrist](mailto:ojiidotch@gmail.com)
-* [Osaetin Daniel](mailto:osaetindaniel@gmail.com)
-* [Sunil Kapil](mailto:snlkapil@gmail.com)
-* [Vishwas B Sharma](mailto:sharma.vishwas88@gmail.com)
+
+- [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 KataniÄ](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 RodrÃguez](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)