Do not crash when failing to read an entry (#1090)

[etc/vim.git] / README.md

diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -1,39 +1,51 @@
-![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)
+

 <h2 align="center">The Uncompromising Code Formatter</h2>
 
 <p align="center">
 <h2 align="center">The Uncompromising Code Formatter</h2>
 
 <p align="center">

-<a href="https://travis-ci.org/ambv/black"><img alt="Build Status" src="https://travis-ci.org/ambv/black.svg?branch=master"></a>
-<a href="http://black.readthedocs.io/en/latest/?badge=latest"><img alt="Documentation Status" src="http://readthedocs.org/projects/black/badge/?version=latest"></a>
-<a href="https://coveralls.io/github/ambv/black?branch=master"><img alt="Coverage Status" src="https://coveralls.io/repos/github/ambv/black/badge.svg?branch=master"></a>
-<a href="https://github.com/ambv/black/blob/master/LICENSE"><img alt="License: MIT" src="http://black.readthedocs.io/en/latest/_static/license.svg"></a>
-<a href="https://pypi.python.org/pypi/black"><img alt="PyPI" src="http://black.readthedocs.io/en/latest/_static/pypi.svg"></a>
-<a href="https://github.com/ambv/black"><img alt="Code style: black" src="https://img.shields.io/badge/code%20style-black-000000.svg"></a>
+<a href="https://travis-ci.com/psf/black"><img alt="Build Status" src="https://travis-ci.com/psf/black.svg?branch=master"></a>
+<a href="https://black.readthedocs.io/en/stable/?badge=stable"><img alt="Documentation Status" src="https://readthedocs.org/projects/black/badge/?version=stable"></a>
+<a href="https://coveralls.io/github/psf/black?branch=master"><img alt="Coverage Status" src="https://coveralls.io/repos/github/psf/black/badge.svg?branch=master"></a>
+<a href="https://github.com/psf/black/blob/master/LICENSE"><img alt="License: MIT" src="https://black.readthedocs.io/en/stable/_static/license.svg"></a>
+<a href="https://pypi.org/project/black/"><img alt="PyPI" src="https://black.readthedocs.io/en/stable/_static/pypi.svg"></a>
+<a href="https://pepy.tech/project/black"><img alt="Downloads" src="https://pepy.tech/badge/black"></a>
+<a href="https://github.com/psf/black"><img alt="Code style: black" src="https://img.shields.io/badge/code%20style-black-000000.svg"></a>

 </p>
 
 > “Any color you like.”
 
 </p>
 
 > “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.

 
 

-*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.
+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)** | **[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
+---

 
 

-*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 and usage

 
 

+### Installation
+
+_Black_ can be installed by running `pip install black`. It requires Python 3.6.0+ to
+run but you can reformat Python 2 code with it, too.

 
 ### Usage
 
 
 ### Usage
 


@@ -45,109 +57,144 @@ black {source_file_or_directory}
 
 ### Command line options
 
 
 ### 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:
 
 ```text
 black [OPTIONS] [SRC]...
 
 Options:

-  -l, --line-length INTEGER   Where to wrap around.  [default: 88]
-  --check                     Don't write the files back, just return the
-                              status.  Return code 0 means nothing would
-                              change.  Return code 1 means some files would be
-                              reformatted.  Return code 123 means there was an
-                              internal error.
-  --diff                      Don't write the files back, just output a diff
-                              for each file on stdout.
-  --fast / --safe             If --fast given, skip temporary sanity checks.
-                              [default: --safe]
-  --version                   Show the version and exit.
-  --help                      Show this message and exit.
-```
-
-*Black* is a well-behaved Unix-style command-line tool:
-* it does nothing if no sources are passed to it;
-* it will read from standard input and write to standard output if `-`
-  is used as the filename;
-* it only outputs messages to users on standard error;
-* exits with code 0 unless an internal error occured (or `--check` was
-  used).
-
-
-### NOTE: This is an early pre-release
-
-*Black* can already successfully format itself and the standard library.
-It also sports a decent test suite.  However, it is still very new.
-Things will probably be wonky for a while. This is made explicit by the
-"Alpha" trove classifier, as well as by the "a" in the version number.
-What this means for you is that **until the formatter becomes stable,
-you should expect some formatting to change in the future**.
-
-Also, as a temporary safety measure, *Black* will check that the
-reformatted code still produces a valid AST that is equivalent to the
-original.  This slows it down.  If you're feeling confident, use
-``--fast``.
-
-
-## The *Black* code style
-
-*Black* reformats entire files in place.  It is not configurable.  It
-doesn't take previous formatting into account.  It doesn't reformat
-blocks that start with `# fmt: off` and end with `# fmt: on`.  It also
-recognizes [YAPF](https://github.com/google/yapf)'s block comments to
-the same effect, as a courtesy for straddling code.
-
-
-### How *Black* wraps lines
-
-*Black* ignores previous formatting and applies uniform horizontal
-and vertical whitespace to your code.  The rules for horizontal
-whitespace are pretty obvious and can be summarized as: do whatever
-makes `pycodestyle` happy.  The coding style used by *Black* can be
-viewed as a strict subset of PEP 8.
-
-As for vertical whitespace, *Black* tries to render one full expression
-or simple statement per line.  If this fits the allotted line length,
-great.
+  -c, --code TEXT                 Format the code passed in as a string.
+  -l, --line-length INTEGER       How many characters per line to allow.
+                                  [default: 88]
+  -t, --target-version [py27|py33|py34|py35|py36|py37|py38]
+                                  Python versions that should be supported by
+                                  Black's output. [default: per-file auto-
+                                  detection]
+  --py36                          Allow using Python 3.6-only syntax on all
+                                  input files.  This will put trailing commas
+                                  in function signatures and calls also after
+                                  *args and **kwargs. Deprecated; use
+                                  --target-version instead. [default: per-file
+                                  auto-detection]
+  --pyi                           Format all input files like typing stubs
+                                  regardless of file extension (useful when
+                                  piping source on standard input).
+  -S, --skip-string-normalization
+                                  Don't normalize string quotes or prefixes.
+  --check                         Don't write the files back, just return the
+                                  status.  Return code 0 means nothing would
+                                  change.  Return code 1 means some files
+                                  would be reformatted.  Return code 123 means
+                                  there was an internal error.
+  --diff                          Don't write the files back, just output a
+                                  diff for each file on stdout.
+  --fast / --safe                 If --fast given, skip temporary sanity
+                                  checks. [default: --safe]
+  --include TEXT                  A regular expression that matches files and
+                                  directories that should be included on
+                                  recursive searches.  An empty value means
+                                  all files are included regardless of the
+                                  name.  Use forward slashes for directories
+                                  on all platforms (Windows, too).  Exclusions
+                                  are calculated first, inclusions later.
+                                  [default: \.pyi?$]
+  --exclude TEXT                  A regular expression that matches files and
+                                  directories that should be excluded on
+                                  recursive searches.  An empty value means no
+                                  paths are excluded. Use forward slashes for
+                                  directories on all platforms (Windows, too).
+                                  Exclusions are calculated first, inclusions
+                                  later.  [default: /(\.eggs|\.git|\.hg|\.mypy
+                                  _cache|\.nox|\.tox|\.venv|_build|buck-
+                                  out|build|dist)/]
+  -q, --quiet                     Don't emit non-error messages to stderr.
+                                  Errors are still emitted, silence those with
+                                  2>/dev/null.
+  -v, --verbose                   Also emit messages to stderr about files
+                                  that were not changed or were ignored due to
+                                  --exclude=.
+  --version                       Show the version and exit.
+  --config PATH                   Read configuration from PATH.
+  -h, --help                      Show this message and exit.
+```
+
+_Black_ is a well-behaved Unix-style command-line tool:
+
+- it does nothing if no sources are passed to it;
+- it will read from standard input and write to standard output if `-` is used as the
+  filename;
+- it only outputs messages to users on standard error;
+- exits with code 0 unless an internal error occurred (or `--check` was used).
+
+### NOTE: This is a beta product
+
+_Black_ is already [successfully used](#used-by) by many projects, small and big. It
+also sports a decent test suite. However, it is still very new. Things will probably be
+wonky for a while. This is made explicit by the "Beta" trove classifier, as well as by
+the "b" in the version number. What this means for you is that **until the formatter
+becomes stable, you should expect some formatting to change in the future**. That being
+said, no drastic stylistic changes are planned, mostly responses to bug reports.
+
+Also, as a temporary safety measure, _Black_ will check that the reformatted code still
+produces a valid AST that is equivalent to the original. This slows it down. If you're
+feeling confident, use `--fast`.
+
+## The _Black_ code style
+
+_Black_ reformats entire files in place. It is not configurable. It doesn't take
+previous formatting into account. It doesn't reformat blocks that start with
+`# fmt: off` and end with `# fmt: on`. `# fmt: on/off` have to be on the same level of
+indentation. It also recognizes [YAPF](https://github.com/google/yapf)'s block comments
+to the same effect, as a courtesy for straddling code.
+
+### How _Black_ wraps lines
+
+_Black_ ignores previous formatting and applies uniform horizontal and vertical
+whitespace to your code. The rules for horizontal whitespace can be summarized as: do
+whatever makes `pycodestyle` happy. The coding style used by _Black_ can be viewed as a
+strict subset of PEP 8.
+
+As for vertical whitespace, _Black_ tries to render one full expression or simple
+statement per line. If this fits the allotted line length, great.
+

 ```py3
 # in:
 
 ```py3
 # in:
 

-l = [1,
+j = [1,

      2,
      3,
 ]
 
 # out:
 
      2,
      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:
 
 ```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:
 
 
 # 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:
 
 ```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:
         ...
     """Applies `variables` to the `template` and writes to `file`."""
     with open(file, 'w') as f:
         ...


@@ -158,6 +205,8 @@ def very_important_function(
     template: str,
     *variables,
     file: os.PathLike,
     template: str,
     *variables,
     file: os.PathLike,

+    engine: str,
+    header: bool = True,

     debug: bool = False,
 ):
     """Applies `variables` to the `template` and writes to `file`."""
     debug: bool = False,
 ):
     """Applies `variables` to the `template` and writes to `file`."""


@@ -165,203 +214,722 @@ 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.
+
+<details>
+<summary>A compatible `.isort.cfg`</summary>
+
+```
+[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 ]
+```
+
+</details>

 
 ### Line length
 
 
 ### 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
 ```ini
 [flake8]
 max-line-length = 80
 ...
 select = C,E,F,W,B,B950

-ignore = E501
+ignore = E501,W503,E203

 ```
 
 ```
 

-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. 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".

 
 ### Empty lines
 
 
 ### Empty lines
 

-*Black* avoids spurious vertical whitespace.  This is in the spirit of
-PEP 8 which says that in-function vertical whitespace should only be
-used sparingly.  One exception is control flow statements: *Black* will
-always emit an extra empty line after ``return``, ``raise``, ``break``,
-``continue``, and ``yield``.  This is to make changes in control flow
-more prominent to readers of your code.
+_Black_ 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.  *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.
+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
 
 
 ### 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
 
 
 ### 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_ prefers double quotes (`"` and `"""`) over single quotes (`'` and `'''`). It
+will replace the latter with the former as long as it does not result in more backslash
+escapes than before.
+
+_Black_ also standardizes string prefixes, making them always lowercase. On top of that,
+if your code is already Python 3.6+ only or it's using the `unicode_literals` future
+import, _Black_ will remove `u` from the string prefix as it is meaningless in those
+scenarios.
+
+The main reason to standardize on a single form of quotes is aesthetics. Having one kind
+of quotes everywhere reduces reader distraction. It will also enable a future version of
+_Black_ to merge consecutive string literals that ended up on the same line (see
+[#26](https://github.com/psf/black/issues/26) for details).
+
+Why settle on double quotes? They anticipate apostrophes in English text. They match the
+docstring standard described in
+[PEP 257](https://www.python.org/dev/peps/pep-0257/#what-is-a-docstring). An empty
+string in double quotes (`""`) is impossible to confuse with a one double-quote
+regardless of fonts and syntax highlighting used. On top of this, double quotes for
+strings are consistent with C which Python interacts a lot with.
+
+On certain keyboard layouts like US English, typing single quotes is a bit easier than
+double quotes. The latter requires use of the Shift key. My recommendation here is to
+keep using whatever is faster to type and let _Black_ handle the transformation.
+
+If you are adopting _Black_ in a large project with pre-existing string conventions
+(like the popular
+["single quotes for data, double quotes for human-readable strings"](https://stackoverflow.com/a/56190)),
+you can pass `--skip-string-normalization` on the command line. This is meant as an
+adoption helper, avoid using this for new projects.
+
+### Numeric literals
+
+_Black_ standardizes most numeric literals to use lowercase letters for the syntactic
+parts and uppercase letters for the digits themselves: `0xAB` instead of `0XAB` and
+`1e10` instead of `1E10`. Python 2 long literals are styled as `2L` instead of `2l` to
+avoid confusion between `l` and `1`.
+
+### Line breaks & binary operators
+
+_Black_ will break a line before a binary operator when splitting a block of code over
+multiple lines. This is so that _Black_ is compliant with the recent changes in the
+[PEP 8](https://www.python.org/dev/peps/pep-0008/#should-a-line-break-before-or-after-a-binary-operator)
+style guide, which emphasizes that this approach improves readability.
+
+This behaviour may raise `W503 line break before binary operator` warnings in style
+guide enforcement tools like Flake8. Since `W503` is not PEP 8 compliant, you should
+tell Flake8 to ignore these warnings.
+
+### Slices
+
+PEP 8
+[recommends](https://www.python.org/dev/peps/pep-0008/#whitespace-in-expressions-and-statements)
+to treat `:` in slices as a binary operator with the lowest priority, and to leave an
+equal amount of space on either side, except if a parameter is omitted (e.g.
+`ham[1 + 1 :]`). It also states that for extended slices, both `:` operators have to
+have the same amount of spacing, except if a parameter is omitted (`ham[1 + 1 ::]`).
+_Black_ enforces these rules consistently.
+
+This behaviour may raise `E203 whitespace before ':'` warnings in style guide
+enforcement tools like Flake8. Since `E203` is not PEP 8 compliant, you should tell
+Flake8 to ignore these warnings.
+
+### Parentheses
+
+Some parentheses are optional in the Python grammar. Any expression can be wrapped in a
+pair of parentheses to form an atom. There are a few interesting cases:
+
+- `if (...):`
+- `while (...):`
+- `for (...) in (...):`
+- `assert (...), (...)`
+- `from X import (...)`
+- assignments like:
+  - `target = (...)`
+  - `target: type = (...)`
+  - `some, *un, packing = (...)`
+  - `augmented += (...)`
+
+In those cases, parentheses are removed when the entire statement fits in one line, or
+if the inner expression doesn't have any delimiters to further split on. If there is
+only a single delimiter and the expression starts or ends with a bracket, the
+parenthesis can also be successfully omitted since the existing bracket pair will
+organize the expression neatly anyway. Otherwise, the parentheses are added.
+
+Please note that _Black_ does not add or remove any additional nested parentheses that
+you might want to have for clarity or further code organization. For example those
+parentheses are not going to be removed:

 
 

-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).
+```py3
+return not (this or that)
+decision = (maybe.this() and values > 0) or (maybe.that() and values < 0)
+```
+
+### Call chains
+
+Some popular APIs, like ORMs, use call chaining. This API style is known as a
+[fluent interface](https://en.wikipedia.org/wiki/Fluent_interface). _Black_ formats
+those by treating dots that follow a call or an indexing operation like a very low
+priority delimiter. It's easier to show the behavior than to explain it. Look at the
+example:
+
+```py3
+def example(session):
+    result = (
+        session.query(models.Customer.id)
+        .filter(
+            models.Customer.account_id == account_id,
+            models.Customer.email == email_address,
+        )
+        .order_by(models.Customer.id.asc())
+        .all()
+    )
+```
+
+### Typing stub files
+
+PEP 484 describes the syntax for type hints in Python. One of the use cases for typing
+is providing type annotations for modules which cannot contain them directly (they might
+be written in C, or they might be third-party, or their implementation may be overly
+dynamic, and so on).
+
+To solve this,
+[stub files with the `.pyi` file extension](https://www.python.org/dev/peps/pep-0484/#stub-files)
+can be used to describe typing information for an external module. Those stub files omit
+the implementation of classes and functions they describe, instead they only contain the
+structure of the file (listing globals, functions, and classes with their members). The
+recommended code style for those files is more terse than PEP 8:
+
+- prefer `...` on the same line as the class/function signature;
+- avoid vertical whitespace between consecutive module-level functions, names, or
+  methods and fields within a single class;
+- use a single blank line between top-level class definitions, or none if the classes
+  are very small.
+
+_Black_ enforces the above rules. There are additional guidelines for formatting `.pyi`
+file that are not enforced yet but might be in a future version of the formatter:
+
+- all function bodies should be empty (contain `...` instead of the body);
+- do not use docstrings;
+- prefer `...` over `pass`;
+- for arguments with a default, use `...` instead of the actual default;
+- avoid using string literals in type annotations, stub files support forward references
+  natively (like Python 3.7 code with `from __future__ import annotations`);
+- use variable annotations instead of type comments, even for stubs that target older
+  versions of Python;
+- for arguments that default to `None`, use `Optional[]` explicitly;
+- use `float` instead of `Union[int, float]`.
+
+## 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.
+
+<details>
+<summary>Example `pyproject.toml`</summary>
+
+```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
+)
+'''
+```

 
 

-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.
+</details>

 
 

-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.
+### Lookup hierarchy

 
 

+Command-line options have defaults that you can see in `--help`. A `pyproject.toml` can
+override those defaults. Finally, options provided by the user on the command line
+override both.
+
+_Black_ will only ever use one `pyproject.toml` file during an entire run. It doesn't
+look for multiple files, and doesn't compose configuration from different levels of the
+file hierarchy.

 
 ## Editor integration
 
 ### Emacs
 
 
 ## Editor integration
 
 ### Emacs
 

-Use [proofit404/blacken](https://github.com/proofit404/blacken).
+Use [proofit404/blacken](https://github.com/proofit404/blacken) or
+[Elpy](https://github.com/jorgenschaefer/elpy).
+
+### PyCharm/IntelliJ IDEA
+
+1. Install `black`.
+
+```console
+$ pip install black
+```
+
+2. Locate your `black` installation folder.
+
+On macOS / Linux / BSD:
+
+```console
+$ which black
+/usr/local/bin/black  # possible location
+```
+
+On Windows:
+
+```console
+$ where black
+%LocalAppData%\Programs\Python\Python36-32\Scripts\black.exe  # possible location
+```
+
+3. Open External tools in PyCharm/IntelliJ IDEA
+
+On macOS:
+
+`PyCharm -> Preferences -> Tools -> External Tools`
+
+On Windows / Linux / BSD:
+
+`File -> Settings -> Tools -> External Tools`
+
+4. Click the + icon to add a new external tool with the following values:

 
 

+   - Name: Black
+   - Description: Black is the uncompromising Python code formatter.
+   - Program: <install_location_from_step_2>
+   - Arguments: `"$FilePath$"`
+
+5. Format the currently opened file by selecting `Tools -> External Tools -> black`.
+
+   - Alternatively, you can set a keyboard shortcut by navigating to
+     `Preferences or Settings -> Keymap -> External Tools -> External Tools - Black`.
+
+6. Optionally, run _Black_ on every file save:
+
+   1. Make sure you have the
+      [File Watcher](https://plugins.jetbrains.com/plugin/7177-file-watchers) plugin
+      installed.
+   2. Go to `Preferences or Settings -> Tools -> File Watchers` and click `+` to add a
+      new watcher:
+      - Name: Black
+      - File type: Python
+      - Scope: Project Files
+      - Program: <install_location_from_step_2>
+      - Arguments: `$FilePath$`
+      - Output paths to refresh: `$FilePath$`
+      - Working directory: `$ProjectFileDir$`
+
+   - Uncheck "Auto-save edited files to trigger the watcher"
+
+### Wing IDE
+
+Wing supports black via the OS Commands tool, as explained in the Wing documentation on
+[pep8 formatting](https://wingware.com/doc/edit/pep8). The detailed procedure is:
+
+1. Install `black`.
+
+```console
+$ pip install black
+```
+
+2. Make sure it runs from the command line, e.g.
+
+```console
+$ black --help
+```
+
+3. In Wing IDE, activate the **OS Commands** panel and define the command **black** to
+   execute black on the currently selected file:
+
+- Use the Tools -> OS Commands menu selection
+- click on **+** in **OS Commands** -> New: Command line..
+  - Title: black
+  - Command Line: black %s
+  - I/O Encoding: Use Default
+  - Key Binding: F1
+  - [x] Raise OS Commands when executed
+  - [x] Auto-save files before execution
+  - [x] Line mode
+
+4. Select a file in the editor and press **F1** , or whatever key binding you selected
+   in step 3, to reformat the file.

 
 ### Vim
 
 Commands and shortcuts:
 
 
 ### Vim
 
 Commands and shortcuts:
 

-* `,=` or `:Black` to format the entire file (ranges not supported);
-* `:BlackUpgrade` to upgrade *Black* inside the virtualenv;
-* `:BlackVersion` to get the current version of *Black* inside the
-  virtualenv.
+- `:Black` to format the entire file (ranges not supported);
+- `:BlackUpgrade` to upgrade _Black_ inside the virtualenv;
+- `:BlackVersion` to get the current version of _Black_ inside the virtualenv.

 
 Configuration:
 
 Configuration:

-* `g:black_fast` (defaults to `0`)
-* `g:black_linelength` (defaults to `88`)
-* `g:black_virtualenv` (defaults to `~/.vim/black`)

 
 

-To install, copy the plugin from [vim/plugin/black.vim](https://github.com/ambv/black/tree/master/vim/plugin/black.vim).
-Let me know if this requires any changes to work with Vim 8's builtin
-`packadd`, or Pathogen, or Vundle, and so on.
+- `g:black_fast` (defaults to `0`)
+- `g:black_linelength` (defaults to `88`)
+- `g:black_skip_string_normalization` (defaults to `0`)
+- `g:black_virtualenv` (defaults to `~/.vim/black` or `~/.local/share/nvim/black`)
+
+To install with [vim-plug](https://github.com/junegunn/vim-plug):
+
+```
+Plug 'psf/black'
+```
+
+or with [Vundle](https://github.com/VundleVim/Vundle.vim):
+
+```
+Plugin 'psf/black'
+```
+
+or you can copy the plugin from
+[plugin/black.vim](https://github.com/psf/black/tree/master/plugin/black.vim).
+
+```
+mkdir -p ~/.vim/pack/python/start/black/plugin
+curl https://raw.githubusercontent.com/psf/black/master/plugin/black.vim -o ~/.vim/pack/python/start/black/plugin/black.vim
+```
+
+Let me know if this requires any changes to work with Vim 8's builtin `packadd`, or
+Pathogen, and so on.
+
+This plugin **requires Vim 7.0+ built with Python 3.6+ support**. It needs Python 3.6 to
+be able to run _Black_ inside the Vim process which is much faster than calling an
+external command.

 
 

-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.

 
 

-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.

 
 

-If you need to do anything special to make your virtualenv work and
-install *Black* (for example you want to run a version from master), just
-create a virtualenv manually and point `g:black_virtualenv` to it.
-The plugin will use it.
+To run _Black_ on save, add the following line to `.vimrc` or `init.vim`:

 
 

-**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.
+```
+autocmd BufWritePre *.py execute ':Black'
+```
+
+To run _Black_ on a key press (e.g. F9 below), add this:
+
+```
+nnoremap <F9> :Black<CR>
+```

 
 

+**How to get Vim with Python 3.6?** On Ubuntu 17.10 Vim comes with Python 3.6 by
+default. On macOS with Homebrew run: `brew install vim --with-python3`. When building
+Vim from source, use: `./configure --enable-python3interp=yes`. There's many guides
+online how to do this.

 
 ### Visual Studio Code
 
 
 ### Visual Studio Code
 

-Use [joslarson.black-vscode](https://marketplace.visualstudio.com/items?itemName=joslarson.black-vscode).
+Use the
+[Python extension](https://marketplace.visualstudio.com/items?itemName=ms-python.python)
+([instructions](https://code.visualstudio.com/docs/python/editing#_formatting)).
+
+### SublimeText 3
+
+Use [sublack plugin](https://github.com/jgirardet/sublack).
+
+### Jupyter Notebook Magic
+
+Use [blackcellmagic](https://github.com/csurfer/blackcellmagic).
+
+### Python Language Server
+
+If your editor supports the [Language Server Protocol](https://langserver.org/) (Atom,
+Sublime Text, Visual Studio Code and many more), you can use the
+[Python Language Server](https://github.com/palantir/python-language-server) with the
+[pyls-black](https://github.com/rupert/pyls-black) plugin.
+
+### Atom/Nuclide
+
+Use [python-black](https://atom.io/packages/python-black).
+
+### Kakoune

 
 

+Add the following hook to your kakrc, then run black with `:format`.
+
+```
+hook global WinSetOption filetype=python %{
+    set-option window formatcmd 'black -q  -'
+}
+```

 
 ### Other editors
 
 
 ### Other editors
 

-Atom/Nuclide integration is planned by the author, others will
-require external contributions.
+Other editors will require external contributions.

 
 Patches welcome! ✨ 🍰 ✨
 
 
 Patches welcome! ✨ 🍰 ✨
 

-Any tool that can pipe code through *Black* using its stdio mode (just
-[use `-` as the file name](http://www.tldp.org/LDP/abs/html/special-chars.html#DASHREF2)).
-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.
+Any tool that can pipe code through _Black_ using its stdio mode (just
+[use `-` as the file name](https://www.tldp.org/LDP/abs/html/special-chars.html#DASHREF2)).
+The formatted code will be returned on stdout (unless `--check` was passed). _Black_
+will still emit messages on stderr but that shouldn't affect your use case.
+
+This can be used for example with PyCharm's or IntelliJ's
+[File Watchers](https://www.jetbrains.com/help/pycharm/file-watchers.html).
+
+## blackd
+
+`blackd` is a small HTTP server that exposes _Black_'s functionality over a simple
+protocol. The main benefit of using it is to avoid paying the cost of starting up a new
+_Black_ process every time you want to blacken a file.
+
+### Usage
+
+`blackd` is not packaged alongside _Black_ by default because it has additional
+dependencies. You will need to do `pip install black[d]` to install it.
+
+You can start the server on the default port, binding only to the local interface by
+running `blackd`. You will see a single line mentioning the server's version, and the
+host and port it's listening on. `blackd` will then print an access log similar to most
+web servers on standard output, merged with any exception traces caused by invalid
+formatting requests.
+
+`blackd` provides even less options than _Black_. You can see them by running
+`blackd --help`:
+
+```text
+Usage: blackd [OPTIONS]
+
+Options:
+  --bind-host TEXT                Address to bind the server to.
+  --bind-port INTEGER             Port to listen on
+  --version                       Show the version and exit.
+  -h, --help                      Show this message and exit.
+```
+
+There is no official blackd client tool (yet!). You can test that blackd is working
+using `curl`:
+
+```
+blackd --bind-port 9090 &  # or let blackd choose a port
+curl -s -XPOST "localhost:9090" -d "print('valid')"
+```
+
+### Protocol
+
+`blackd` only accepts `POST` requests at the `/` path. The body of the request should
+contain the python source code to be formatted, encoded according to the `charset` field
+in the `Content-Type` request header. If no `charset` is specified, `blackd` assumes
+`UTF-8`.
+
+There are a few HTTP headers that control how the source is formatted. These correspond
+to command line flags for _Black_. There is one exception to this: `X-Protocol-Version`
+which if present, should have the value `1`, otherwise the request is rejected with
+`HTTP 501` (Not Implemented).
+
+The headers controlling how code is formatted are:
+
+- `X-Line-Length`: corresponds to the `--line-length` command line flag.
+- `X-Skip-String-Normalization`: corresponds to the `--skip-string-normalization`
+  command line flag. If present and its value is not the empty string, no string
+  normalization will be performed.
+- `X-Fast-Or-Safe`: if set to `fast`, `blackd` will act as _Black_ does when passed the
+  `--fast` command line flag.
+- `X-Python-Variant`: if set to `pyi`, `blackd` will act as _Black_ does when passed the
+  `--pyi` command line flag. Otherwise, its value must correspond to a Python version or
+  a set of comma-separated Python versions, optionally prefixed with `py`. For example,
+  to request code that is compatible with Python 3.5 and 3.6, set the header to
+  `py3.5,py3.6`.
+
+If any of these headers are set to invalid values, `blackd` returns a `HTTP 400` error
+response, mentioning the name of the problematic header in the message body.
+
+Apart from the above, `blackd` can produce the following response codes:
+
+- `HTTP 204`: If the input is already well-formatted. The response body is empty.
+- `HTTP 200`: If formatting was needed on the input. The response body contains the
+  blackened Python code, and the `Content-Type` header is set accordingly.
+- `HTTP 400`: If the input contains a syntax error. Details of the error are returned in
+  the response body.
+- `HTTP 500`: If there was any kind of error while trying to format the input. The
+  response body contains a textual representation of the error.
+
+The response headers include a `X-Black-Version` header containing the version of
+_Black_.
+
+## Version control integration
+
+Use [pre-commit](https://pre-commit.com/). Once you
+[have it installed](https://pre-commit.com/#install), add this to the
+`.pre-commit-config.yaml` in your repository:
+
+```yaml
+repos:
+  - repo: https://github.com/psf/black
+    rev: stable
+    hooks:
+      - id: black
+        language_version: python3.6
+```
+
+Then run `pre-commit install` and you're ready to go.
+
+Avoid using `args` in the hook. Instead, store necessary configuration in
+`pyproject.toml` so that editors and command-line usage of Black all behave consistently
+for your project. See _Black_'s own [pyproject.toml](/pyproject.toml) for an example.
+
+If you're already using Python 3.7, switch the `language_version` accordingly. Finally,
+`stable` is a tag that is pinned to the latest release on PyPI. If you'd rather run on
+master, this is also an option.
+
+## Ignoring unmodified files
+
+_Black_ remembers files it has already formatted, unless the `--diff` flag is used or
+code is passed via standard input. This information is stored per-user. The exact
+location of the file depends on the _Black_ version and the system on which _Black_ is
+run. The file is non-portable. The standard location on common operating systems is:

 
 

-This can be used for example with PyCharm's [File Watchers](https://www.jetbrains.com/help/pycharm/file-watchers.html).
+- Windows:
+  `C:\\Users\<username>\AppData\Local\black\black\Cache\<version>\cache.<line-length>.<file-mode>.pickle`
+- macOS:
+  `/Users/<username>/Library/Caches/black/<version>/cache.<line-length>.<file-mode>.pickle`
+- Linux:
+  `/home/<username>/.cache/black/<version>/cache.<line-length>.<file-mode>.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/<version>/`.
+
+## Used by
+
+The following notable open-source projects trust _Black_ with enforcing a consistent
+code style: pytest, tox, Pyramid, Django Channels, Hypothesis, attrs, SQLAlchemy,
+Poetry, PyPA applications (Warehouse, Pipenv, virtualenv), pandas, Pillow, every Datadog
+Agent Integration.
+
+Are we missing anyone? Let us know.

 
 ## Testimonials
 
 
 ## Testimonials
 

-**Dusty Phillips**, [writer](https://smile.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dusty+phillips):
+**Dusty Phillips**,
+[writer](https://smile.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dusty+phillips):

 
 

-> Black is opinionated so you don't have to be.
+> _Black_ is opinionated so you don't have to be.

 
 

-**Hynek Schlawack**, [creator of `attrs`](http://www.attrs.org/), core
-developer of Twisted and CPython:
+**Hynek Schlawack**, [creator of `attrs`](https://www.attrs.org/), core developer of
+Twisted and CPython:

 
 > An auto-formatter that doesn't suck is all I want for Xmas!
 
 
 > An auto-formatter that doesn't suck is all I want for Xmas!
 


@@ -369,178 +937,503 @@ developer of Twisted and CPython:
 
 > At least the name is good.
 
 
 > At least the name is good.
 

-**Kenneth Reitz**, creator of [`requests`](http://python-requests.org/)
-and [`pipenv`](https://docs.pipenv.org/):
+**Kenneth Reitz**, creator of [`requests`](http://python-requests.org/) and
+[`pipenv`](https://docs.pipenv.org/):

 
 > This vastly improves the formatting of our code. Thanks a ton!
 
 
 > This vastly improves the formatting of our code. Thanks a ton!
 

-

 ## Show your style
 
 Use the badge in your project's README.md:
 
 ```markdown
 ## 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/ambv/black)
+[![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)

 ```
 
 ```
 

-Looks like this: [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/ambv/black)
+Using the badge in README.rst:

 
 

+```
+.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
+    :target: https://github.com/psf/black
+```
+
+Looks like this:
+[![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black)

 
 ## License
 
 MIT
 
 
 ## License
 
 MIT
 

+## Contributing to _Black_

 
 

-## Contributing to Black
-
-In terms of inspiration, *Black* is about as configurable as *gofmt* and
-*rustfmt* are.  This is deliberate.
+In terms of inspiration, _Black_ is about as configurable as _gofmt_. This is
+deliberate.

 
 

-Bug reports and fixes are always welcome!  However, before you suggest a
-new feature or configuration knob, ask yourself why you want it.  If it
-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.
+Bug reports and fixes are always welcome! However, before you suggest a new feature or
+configuration knob, ask yourself why you want it. If it enables better integration with
+some workflow, fixes an inconsistency, speeds things up, and so on - go for it! On the
+other hand, if your answer is "because I don't like a particular formatting" then you're
+not ready to embrace _Black_ yet. Such changes are unlikely to get accepted. You can
+still try but prepare to be disappointed.

 
 More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
 
 
 More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
 

-

 ## Change Log
 
 ## Change Log
 

-### 18.4a0
+### unreleased
+
+- added `black -c` as a way to format code passed from the command line (#761)
+
+- --safe now works with Python 2 code (#840)
+
+- fixed grammar selection for Python 2-specific code (#765)
+
+- fixed feature detection for trailing commas in function definitions and call sites
+  (#763)
+
+- _Black_ can now format async generators (#593)
+
+- _Black_ no longer crashes on Windows machines with more than 61 cores (#838)
+
+- _Black_ no longer crashes on standalone comments prepended with a backslash (#767)
+
+- _Black_ no longer crashes on `from` ... `import` blocks with comments (#829)
+
+- removed unnecessary parentheses around `yield` expressions (#834)
+
+- added parentheses around long tuples in unpacking assignments (#832)
+
+- fixed bug that led _Black_ format some code with a line length target of 1 (#762)
+
+- _Black_ no longer introduces quotes in f-string subexpressions on string boundaries
+  (#863)
+
+- if _Black_ puts parenthesis around a single expression, it moves comments to the
+  wrapped expression instead of after the brackets (#872)
+
+- _Black_ is now able to format Python code that uses assignment expressions (`:=` as
+  described in PEP-572) (#935)
+
+- _Black_ is now able to format Python code that uses positional-only arguments (`/` as
+  described in PEP-570) (#946)
+
+- `blackd` now returns the version of _Black_ in the response headers (#1013)
+
+### 19.3b0
+
+- new option `--target-version` to control which Python versions _Black_-formatted code
+  should target (#618)
+
+- deprecated `--py36` (use `--target-version=py36` instead) (#724)
+
+- _Black_ no longer normalizes numeric literals to include `_` separators (#696)
+
+- long `del` statements are now split into multiple lines (#698)
+
+- type comments are no longer mangled in function signatures
+
+- improved performance of formatting deeply nested data structures (#509)
+
+- _Black_ now properly formats multiple files in parallel on Windows (#632)
+
+- _Black_ now creates cache files atomically which allows it to be used in parallel
+  pipelines (like `xargs -P8`) (#673)
+
+- _Black_ now correctly indents comments in files that were previously formatted with
+  tabs (#262)
+
+- `blackd` now supports CORS (#622)
+
+### 18.9b0
+
+- numeric literals are now formatted by _Black_ (#452, #461, #464, #469):
+
+  - numeric literals are normalized to include `_` separators on Python 3.6+ code
+
+  - added `--skip-numeric-underscore-normalization` to disable the above behavior and
+    leave numeric underscores as they were in the input
+
+  - code with `_` in numeric literals is recognized as Python 3.6+
+
+  - most letters in numeric literals are lowercased (e.g., in `1e10`, `0x01`)
+
+  - hexadecimal digits are always uppercased (e.g. `0xBADC0DE`)
+
+- added `blackd`, see [its documentation](#blackd) for more info (#349)
+
+- adjacent string literals are now correctly split into multiple lines (#463)
+
+- trailing comma is now added to single imports that don't fit on a line (#250)
+
+- cache is now populated when `--check` is successful for a file which speeds up
+  consecutive checks of properly formatted unmodified files (#448)
+
+- whitespace at the beginning of the file is now removed (#399)
+
+- fixed mangling [pweave](http://mpastell.com/pweave/) and
+  [Spyder IDE](https://pythonhosted.org/spyder/) special comments (#532)
+
+- fixed unstable formatting when unpacking big tuples (#267)
+
+- fixed parsing of `__future__` imports with renames (#389)
+
+- fixed scope of `# fmt: off` when directly preceding `yield` and other nodes (#385)
+
+- fixed formatting of lambda expressions with default arguments (#468)
+
+- fixed `async for` statements: _Black_ no longer breaks them into separate lines (#372)
+
+- note: the Vim plugin stopped registering `,=` as a default chord as it turned out to
+  be a bad idea (#415)
+
+### 18.6b4
+
+- hotfix: don't freeze when multiple comments directly precede `# fmt: off` (#371)
+
+### 18.6b3
+
+- typing stub files (`.pyi`) now have blank lines added after constants (#340)
+
+- `# fmt: off` and `# fmt: on` are now much more dependable:
+
+  - they now work also within bracket pairs (#329)
+
+  - they now correctly work across function/class boundaries (#335)
+
+  - they now work when an indentation block starts with empty lines or misaligned
+    comments (#334)
+
+- made Click not fail on invalid environments; note that Click is right but the
+  likelihood we'll need to access non-ASCII file paths when dealing with Python source
+  code is low (#277)
+
+- fixed improper formatting of f-strings with quotes inside interpolated expressions
+  (#322)
+
+- fixed unnecessary slowdown when long list literals where found in a file
+
+- fixed unnecessary slowdown on AST nodes with very many siblings
+
+- fixed cannibalizing backslashes during string normalization
+
+- fixed a crash due to symbolic links pointing outside of the project directory (#338)
+
+### 18.6b2
+
+- added `--config` (#65)
+
+- added `-h` equivalent to `--help` (#316)
+
+- fixed improper unmodified file caching when `-S` was used
+
+- fixed extra space in string unpacking (#305)
+
+- fixed formatting of empty triple quoted strings (#313)
+
+- fixed unnecessary slowdown in comment placement calculation on lines without comments
+
+### 18.6b1
+
+- hotfix: don't output human-facing information on stdout (#299)
+
+- hotfix: don't output cake emoji on non-zero return code (#300)

 
 

-* added `--diff` (#87)
+### 18.6b0

 
 

-* add line breaks before all delimiters, except in cases like commas, to
-  better comply with PEP 8 (#73)
+- added `--include` and `--exclude` (#270)

 
 

-* standardize string literals to use double quotes (almost) everywhere
-  (#75)
+- added `--skip-string-normalization` (#118)

 
 

-* 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)
+- added `--verbose` (#283)

 
 

-* fixed 18.3a4 regression: don't crash and burn on empty lines with
-  trailing whitespace (#80)
+- the header output in `--diff` now actually conforms to the unified diff spec

 
 

-* fixed 18.3a4 regression: `# yapf: disable` usage as trailing comment
-  would cause Black to not emit the rest of the file (#95)
+- fixed long trivial assignments being wrapped in unnecessary parentheses (#273)

 
 

-* when CTRL+C is pressed while formatting many files, Black no longer
-  freaks out with a flurry of asyncio-related exceptions
+- fixed unnecessary parentheses when a line contained multiline strings (#232)

 
 

-* only allow up to two empty lines on module level and only single empty
-  lines within functions (#74)
+- fixed stdin handling not working correctly if an old version of Click was used (#276)

 
 

+- _Black_ now preserves line endings when formatting a file in place (#258)
+
+### 18.5b1
+
+- added `--pyi` (#249)
+
+- added `--py36` (#249)
+
+- Python grammar pickle caches are stored with the formatting caches, making _Black_
+  work in environments where site-packages is not user-writable (#192)
+
+- _Black_ now enforces a PEP 257 empty line after a class-level docstring (and/or
+  fields) and the first method
+
+- fixed invalid code produced when standalone comments were present in a trailer that
+  was omitted from line splitting on a large expression (#237)
+
+- fixed optional parentheses being removed within `# fmt: off` sections (#224)
+
+- fixed invalid code produced when stars in very long imports were incorrectly wrapped
+  in optional parentheses (#234)
+
+- fixed unstable formatting when inline comments were moved around in a trailer that was
+  omitted from line splitting on a large expression (#238)
+
+- fixed extra empty line between a class declaration and the first method if no class
+  docstring or fields are present (#219)
+
+- fixed extra empty line between a function signature and an inner function or inner
+  class (#196)
+
+### 18.5b0
+
+- call chains are now formatted according to the
+  [fluent interfaces](https://en.wikipedia.org/wiki/Fluent_interface) style (#67)
+
+- data structure literals (tuples, lists, dictionaries, and sets) are now also always
+  exploded like imports when they don't fit in a single line (#152)
+
+- slices are now formatted according to PEP 8 (#178)
+
+- parentheses are now also managed automatically on the right-hand side of assignments
+  and return statements (#140)
+
+- math operators now use their respective priorities for delimiting multiline
+  expressions (#148)
+
+- optional parentheses are now omitted on expressions that start or end with a bracket
+  and only contain a single operator (#177)
+
+- empty parentheses in a class definition are now removed (#145, #180)
+
+- string prefixes are now standardized to lowercase and `u` is removed on Python 3.6+
+  only code and Python 2.7+ code with the `unicode_literals` future import (#188, #198,
+  #199)
+
+- typing stub files (`.pyi`) are now formatted in a style that is consistent with PEP
+  484 (#207, #210)
+
+- progress when reformatting many files is now reported incrementally
+
+- fixed trailers (content with brackets) being unnecessarily exploded into their own
+  lines after a dedented closing bracket (#119)
+
+- fixed an invalid trailing comma sometimes left in imports (#185)
+
+- fixed non-deterministic formatting when multiple pairs of removable parentheses were
+  used (#183)
+
+- fixed multiline strings being unnecessarily wrapped in optional parentheses in long
+  assignments (#215)
+
+- fixed not splitting long from-imports with only a single name
+
+- 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.
+
+- fixed crash on dealing with optional parentheses (#193)
+
+- fixed "is", "is not", "in", and "not in" not considered operators for splitting
+  purposes
+
+- fixed crash when dead symlinks where encountered
+
+### 18.4a4
+
+- don't populate the cache on `--check` (#175)
+
+### 18.4a3
+
+- added a "cache"; files already reformatted that haven't changed on disk won't be
+  reformatted again (#109)
+
+- `--check` and `--diff` are no longer mutually exclusive (#149)
+
+- generalized star expression handling, including double stars; this fixes
+  multiplication making expressions "unsafe" for trailing commas (#132)
+
+- _Black_ no longer enforces putting empty lines behind control flow statements (#90)
+
+- _Black_ now splits imports like "Mode 3 + trailing comma" of isort (#127)
+
+- fixed comment indentation when a standalone comment closes a block (#16, #32)
+
+- fixed standalone comments receiving extra empty lines if immediately preceding a
+  class, def, or decorator (#56, #154)
+
+- fixed `--diff` not showing entire path (#130)
+
+- fixed parsing of complex expressions after star and double stars in function calls
+  (#2)
+
+- fixed invalid splitting on comma in lambda arguments (#133)
+
+- fixed missing splits of ternary expressions (#141)
+
+### 18.4a2
+
+- fixed parsing of unaligned standalone comments (#99, #112)
+
+- fixed placement of dictionary unpacking inside dictionary literals (#111)
+
+- Vim plugin now works on Windows, too
+
+- fixed unstable formatting when encountering unnecessarily escaped quotes in a string
+  (#120)
+
+### 18.4a1
+
+- added `--quiet` (#78)
+
+- added automatic parentheses management (#4)
+
+- added [pre-commit](https://pre-commit.com) integration (#103, #104)
+
+- fixed reporting on `--check` with multiple files (#101, #102)
+
+- fixed removing backslash escapes from raw strings (#100, #105)
+
+### 18.4a0
+
+- added `--diff` (#87)
+
+- add line breaks before all delimiters, except in cases like commas, to better comply
+  with PEP 8 (#73)
+
+- standardize string literals to use double quotes (almost) everywhere (#75)
+
+- fixed handling of standalone comments within nested bracketed expressions; _Black_
+  will no longer produce super long lines or put all standalone comments at the end of
+  the expression (#22)
+
+- fixed 18.3a4 regression: don't crash and burn on empty lines with trailing whitespace
+  (#80)
+
+- fixed 18.3a4 regression: `# yapf: disable` usage as trailing comment would cause
+  _Black_ to not emit the rest of the file (#95)
+
+- when CTRL+C is pressed while formatting many files, _Black_ no longer freaks out with
+  a flurry of asyncio-related exceptions
+
+- only allow up to two empty lines on module level and only single empty lines within
+  functions (#74)

 
 ### 18.3a4
 
 
 ### 18.3a4
 

-* `# fmt: off` and `# fmt: on` are implemented (#5)
+- `# fmt: off` and `# fmt: on` are implemented (#5)

 
 

-* automatic detection of deprecated Python 2 forms of print statements
-  and exec statements in the formatted file (#49)
+- automatic detection of deprecated Python 2 forms of print statements and exec
+  statements in the formatted file (#49)

 
 

-* use proper spaces for complex expressions in default values of typed
-  function arguments (#60)
+- use proper spaces for complex expressions in default values of typed function
+  arguments (#60)

 
 

-* only return exit code 1 when --check is used (#50)
+- only return exit code 1 when --check is used (#50)

 
 

-* don't remove single trailing commas from square bracket indexing
-  (#59)
+- don't remove single trailing commas from square bracket indexing (#59)

 
 

-* don't omit whitespace if the previous factor leaf wasn't a math
-  operator (#55)
+- don't omit whitespace if the previous factor leaf wasn't a math operator (#55)

 
 

-* omit extra space in kwarg unpacking if it's the first argument (#46)
+- omit extra space in kwarg unpacking if it's the first argument (#46)

 
 

-* omit extra space in [Sphinx auto-attribute comments](http://www.sphinx-doc.org/en/stable/ext/autodoc.html#directive-autoattribute)
+- omit extra space in
+  [Sphinx auto-attribute comments](http://www.sphinx-doc.org/en/stable/ext/autodoc.html#directive-autoattribute)

   (#68)
 
   (#68)
 

-

 ### 18.3a3
 
 ### 18.3a3
 

-* don't remove single empty lines outside of bracketed expressions
-  (#19)
-
-* added ability to pipe formatting from stdin to stdin (#25)
+- don't remove single empty lines outside of bracketed expressions (#19)

 
 

-* restored ability to format code with legacy usage of `async` as
-  a name (#20, #42)
+- added ability to pipe formatting from stdin to stdin (#25)

 
 

-* even better handling of numpy-style array indexing (#33, again)
+- restored ability to format code with legacy usage of `async` as a name (#20, #42)

 
 

+- even better handling of numpy-style array indexing (#33, again)

 
 ### 18.3a2
 
 
 ### 18.3a2
 

-* changed positioning of binary operators to occur at beginning of lines
-  instead of at the end, following [a recent change to PEP8](https://github.com/python/peps/commit/c59c4376ad233a62ca4b3a6060c81368bd21e85b)
+- changed positioning of binary operators to occur at beginning of lines instead of at
+  the end, following
+  [a recent change to PEP 8](https://github.com/python/peps/commit/c59c4376ad233a62ca4b3a6060c81368bd21e85b)

   (#21)
 
   (#21)
 

-* ignore empty bracket pairs while splitting. This avoids very weirdly
-  looking formattings (#34, #35)
+- ignore empty bracket pairs while splitting. This avoids very weirdly looking
+  formattings (#34, #35)

 
 

-* remove a trailing comma if there is a single argument to a call
+- remove a trailing comma if there is a single argument to a call

 
 

-* if top level functions were separated by a comment, don't put four
-  empty lines after the upper function
+- if top level functions were separated by a comment, don't put four empty lines after
+  the upper function

 
 

-* fixed unstable formatting of newlines with imports
+- fixed unstable formatting of newlines with imports

 
 

-* fixed unintentional folding of post scriptum standalone comments
-  into last statement if it was a simple statement (#18, #28)
+- fixed unintentional folding of post scriptum standalone comments into last statement
+  if it was a simple statement (#18, #28)

 
 

-* fixed missing space in numpy-style array indexing (#33)
-
-* fixed spurious space after star-based unary expressions (#31)
+- fixed missing space in numpy-style array indexing (#33)

 
 

+- fixed spurious space after star-based unary expressions (#31)

 
 ### 18.3a1
 
 
 ### 18.3a1
 

-* added `--check`
-
-* only put trailing commas in function signatures and calls if it's
-  safe to do so. If the file is Python 3.6+ it's always safe, otherwise
-  only safe if there are no `*args` or `**kwargs` used in the signature
-  or call. (#8)
+- added `--check`

 
 

-* fixed invalid spacing of dots in relative imports (#6, #13)
+- only put trailing commas in function signatures and calls if it's safe to do so. If
+  the file is Python 3.6+ it's always safe, otherwise only safe if there are no `*args`
+  or `**kwargs` used in the signature or call. (#8)

 
 

-* fixed invalid splitting after comma on unpacked variables in for-loops
-  (#23)
+- fixed invalid spacing of dots in relative imports (#6, #13)

 
 

-* fixed spurious space in parenthesized set expressions (#7)
+- fixed invalid splitting after comma on unpacked variables in for-loops (#23)

 
 

-* fixed spurious space after opening parentheses and in default
-  arguments (#14, #17)
+- fixed spurious space in parenthesized set expressions (#7)

 
 

-* fixed spurious space after unary operators when the operand was
-  a complex expression (#15)
+- fixed spurious space after opening parentheses and in default arguments (#14, #17)

 
 

+- fixed spurious space after unary operators when the operand was a complex expression
+  (#15)

 
 ### 18.3a0
 
 
 ### 18.3a0
 

-* first published version, Happy 🍰 Day 2018!
+- first published version, Happy 🍰 Day 2018!

 
 

-* alpha quality
-
-* date-versioned (see: https://calver.org/)
+- alpha quality

 
 

+- date-versioned (see: https://calver.org/)

 
 ## Authors
 
 Glued together by [Łukasz Langa](mailto:lukasz@langa.pl).
 
 
 ## Authors
 
 Glued together by [Łukasz Langa](mailto:lukasz@langa.pl).
 

-Maintained with [Carol Willing](mailto:carolcode@willingconsulting.com)
-and [Carl Meyer](mailto:carl@oddbird.net).
+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), and
+[Zsolt Dollenstein](mailto:zsol.zsol@gmail.com).

 
 Multiple contributions by:
 
 Multiple contributions by:

-* [Artem Malyshev](mailto:proofit404@gmail.com)
-* [Daniel M. Capella](mailto:polycitizen@gmail.com)
-* [Eli Treuherz](mailto:eli.treuherz@cgi.com)
-* Hugo van Kemenade
-* [Mika Naylor](mailto:mail@autophagy.io)
-* [Osaetin Daniel](mailto:osaetindaniel@gmail.com)
-* [Zsolt Dollenstein](mailto:zsol.zsol@gmail.com)
+
+- [Anthony Sottile](mailto:asottile@umich.edu)
+- [Artem Malyshev](mailto:proofit404@gmail.com)
+- [Benjamin Woodruff](mailto:github@benjam.info)
+- [Christian Heimes](mailto:christian@python.org)
+- [Daniel M. Capella](mailto:polycitizen@gmail.com)
+- [Eli Treuherz](mailto:eli@treuherz.com)
+- hauntsaninja
+- Hugo van Kemenade
+- [Ivan Katanić](mailto:ivan.katanic@gmail.com)
+- [Jason Fried](mailto:me@jasonfried.info)
+- [Jonas Obrist](mailto:ojiidotch@gmail.com)
+- [Luka Sterbic](mailto:luka.sterbic@gmail.com)
+- [Miguel Gaiowski](mailto:miggaiowski@gmail.com)
+- [Miroslav Shubernetskiy](mailto:miroslav@miki725.com)
+- [Neraste](mailto:neraste.herr10@gmail.com)
+- [Osaetin Daniel](mailto:osaetindaniel@gmail.com)
+- [Peter Bengtsson](mailto:mail@peterbe.com)
+- [Stavros Korokithakis](mailto:hi@stavros.io)
+- [Sunil Kapil](mailto:snlkapil@gmail.com)
+- [Utsav Shah](mailto:ukshah2@illinois.edu)
+- [Vishwas B Sharma](mailto:sharma.vishwas88@gmail.com)
+- [Chuck Wooters](mailto:chuck.wooters@microsoft.com)