Refactor --pyi and --py36 into FileMode

[etc/vim.git] / README.md

diff --git a/README.md b/README.md
index 587afc50d6875bfd44e9d792dfd7042ff0e188c1..fbe1136d9501141663d7c6c7f80dbd26dd19d9d6 100644 (file)
--- a/README.md
+++ b/README.md
@@ -1,12 +1,20 @@
-# black
+![Black Logo](https://raw.githubusercontent.com/ambv/black/master/docs/_static/logo2-readme.png)
+<h2 align="center">The Uncompromising Code Formatter</h2>

 
 

-[![Build Status](https://travis-ci.org/ambv/black.svg?branch=master)](https://travis-ci.org/ambv/black)
+<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/stable/?badge=stable"><img alt="Documentation Status" src="http://readthedocs.org/projects/black/badge/?version=stable"></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/stable/_static/license.svg"></a>
+<a href="https://pypi.python.org/pypi/black"><img alt="PyPI" src="http://black.readthedocs.io/en/stable/_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>
+</p>

 
 

-> Any color you like.
+> “Any color you like.”

 
 
 *Black* is the uncompromising Python code formatter.  By using it, you
 
 
 *Black* is the uncompromising Python code formatter.  By using it, you

-agree to cease control over minutiae of hand-formatting.  In return,
+agree to cede control over minutiae of hand-formatting.  In return,

 *Black* gives you speed, determinism, and freedom from `pycodestyle`
 nagging about formatting.  You will save time and mental energy for
 more important matters.
 *Black* gives you speed, determinism, and freedom from `pycodestyle`
 nagging about formatting.  You will save time and mental energy for
 more important matters.


@@ -18,39 +26,98 @@ content instead.
 *Black* makes code review faster by producing the smallest diffs
 possible.
 
 *Black* makes code review faster by producing the smallest diffs
 possible.
 

+---

 
 

-## NOTE: This is an early pre-release
+*Contents:* **[Installation and usage](#installation-and-usage)** |
+**[The *Black* code style](#the-black-code-style)** |
+**[Editor integration](#editor-integration)** |
+**[Version control integration](#version-control-integration)** |
+**[Ignoring unmodified files](#ignoring-unmodified-files)** |
+**[Testimonials](#testimonials)** |
+**[Show your style](#show-your-style)** |
+**[License](#license)** |
+**[Contributing](#contributing-to-black)** |
+**[Change Log](#change-log)** |
+**[Authors](#authors)**

 
 

-*Black* can already successfully format itself and the standard library.
-It also sports a decent test suite.  However, it is still very new.
-Things will probably be wonky for a while. This is made explicit by the
-"Alpha" trove classifier, as well as by the "a" in the version number.
-What this means for you is that **until the formatter becomes stable,
-you should expect some formatting to change in the future**.
+---

 
 

-Also, as a temporary safety measure, *Black* will check that the
-reformatted code still produces a valid AST that is equivalent to the
-original.  This slows it down.  If you're feeling confident, use
-``--fast``.
+## Installation 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

 
 

-*Black* can be installed by running `pip install black`.
+### Usage

 
 

+To get started right away with sensible defaults:
+
+```
+black {source_file_or_directory}

 ```
 ```

+
+### Command line options
+
+Black doesn't provide many options.  You can list them by running
+`black --help`:
+
+```text

 black [OPTIONS] [SRC]...
 
 Options:
   -l, --line-length INTEGER   Where to wrap around.  [default: 88]
 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]
   --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.
+   --pyi                      Consider all input files typing stubs regardless
+                              of file extension (useful when piping source on
+                              standard input).
+  --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.  [default: per-file auto-detection]

   --version                   Show the version and exit.
   --help                      Show this message and exit.
 ```
 
   --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 occurred (or `--check` was
+  used).
+
+
+### NOTE: This is a beta product

 
 

-## The philosophy behind *Black*
+*Black* is already successfully used by several 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
 
 *Black* reformats entire files in place.  It is not configurable.  It
 doesn't take previous formatting into account.  It doesn't reformat


@@ -59,37 +126,42 @@ recognizes [YAPF](https://github.com/google/yapf)'s block comments to
 the same effect, as a courtesy for straddling code.
 
 
 the same effect, as a courtesy for straddling code.
 
 

-### How *Black* formats files
+### How *Black* wraps lines

 
 *Black* ignores previous formatting and applies uniform horizontal
 and vertical whitespace to your code.  The rules for horizontal
 
 *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.
+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.
 
 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
+```py3

 # in:
 # in:

+

 l = [1,
      2,
      3,
 ]
 
 # out:
 l = [1,
      2,
      3,
 ]
 
 # out:

+

 l = [1, 2, 3]
 ```
 
 If not, *Black* will look at the contents of the first outer matching
 brackets and put that in a separate indented line.
 l = [1, 2, 3]
 ```
 
 If not, *Black* will look at the contents of the first outer matching
 brackets and put that in a separate indented line.

-```!py3
+```py3

 # in:
 # in:

-l = [[n for n in list_bosses()], [n for n in list_employees()]]
+
+TracebackException.from_exception(exc, limit, lookup_lines, capture_locals)

 
 # out:
 
 # out:

-l = [
-    [n for n in list_bosses()], [n for n in list_employees()]
-]
+
+TracebackException.from_exception(
+    exc, limit, lookup_lines, capture_locals
+)

 ```
 
 If that still doesn't fit the bill, it will decompose the internal
 ```
 
 If that still doesn't fit the bill, it will decompose the internal


@@ -99,23 +171,24 @@ 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.
 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
+```py3

 # in:
 # in:

-def very_important_function(template: str, *variables, *, file: os.PathLike, debug: bool = False):
+
+def very_important_function(template: str, *variables, file: os.PathLike, debug: bool = False):

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

+

 def very_important_function(
     template: str,
     *variables,
 def very_important_function(
     template: str,
     *variables,

-    *,

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

-    with open(file, 'w') as f:
+    with open(file, "w") as f:

         ...
 ```
 
         ...
 ```
 


@@ -127,20 +200,30 @@ 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).
 
 indentation level (like the arguments list and the docstring in the
 example above).
 

-Unnecessary trailing commas are removed if an expression fits in one
-line.  This makes it 1% more likely that your line won't exceed the
-allotted line length limit.
+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.

 
 

-*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.
+<details>
+<summary>A compatible `.isort.cfg`</summary>

 
 

-That's it.  The rest of the whitespace formatting rules follow PEP 8 and
-are designed to keep `pycodestyle` quiet.
+```
+[settings]
+multi_line_output=3
+include_trailing_comma=True
+force_grid_wrap=0
+combine_as_imports=True
+line_length=88
+```

 
 

+The equivalent command line is:
+```
+$ isort --multi-line=3 --trailing-comma --force-grid-wrap=0 --combine-as --line-width=88 [ file.py ]
+```
+</details>

 
 ### Line length
 
 
 ### Line length
 


@@ -165,7 +248,7 @@ 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:
 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
+```ini

 [flake8]
 max-line-length = 80
 ...
 [flake8]
 max-line-length = 80
 ...


@@ -179,14 +262,376 @@ 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".
 
 
 bother you if you overdo it by a few km/h".
 
 

-### Editor integration
+### 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* will allow single empty lines inside functions, and single and
+double empty lines on module level left by the original editors, except
+when they're within parenthesized expressions.  Since such expressions
+are always reformatted to fit minimal space, this whitespace is lost.
+
+It will also insert proper spacing before and after function definitions.
+It's one line before and after inner functions and two lines before and
+after module-level functions and classes.  *Black* will not put empty
+lines between function/class definitions and standalone comments that
+immediately precede the given function/class.
+
+*Black* will enforce single empty lines between a class-level docstring
+and the first following field or method.  This conforms to
+[PEP 257](https://www.python.org/dev/peps/pep-0257/#multi-line-docstrings).
+
+*Black* won't insert empty lines after function docstrings unless that
+empty line is required due to an inner function starting immediately
+after.
+
+
+### Trailing commas
+
+*Black* will add trailing commas to expressions that are split
+by comma where each element is on its own line.  This includes function
+signatures.
+
+Unnecessary trailing commas are removed if an expression fits in one
+line.  This makes it 1% more likely that your line won't exceed the
+allotted line length limit.  Moreover, in this scenario, if you added
+another argument to your call, you'd probably fit it in the same line
+anyway.  That doesn't make diffs any larger.
+
+One exception to removing trailing commas is tuple expressions with
+just one element.  In this case *Black* won't touch the single trailing
+comma as this would unexpectedly change the underlying data type.  Note
+that this is also the case when commas are used while indexing.  This is
+a tuple in disguise: ```numpy_array[3, ]```.
+
+One exception to adding trailing commas is function signatures
+containing `*`, `*args`, or `**kwargs`.  In this case a trailing comma
+is only safe to use on Python 3.6.  *Black* will detect if your file is
+already 3.6+ only and use trailing commas in this situation.  If you
+wonder how it knows, it looks for f-strings and existing use of trailing
+commas in function signatures that have stars in them.  In other words,
+if you'd like a trailing comma in this situation and *Black* didn't
+recognize it was safe to do so, put it there manually and *Black* will
+keep it.
+
+
+### Strings
+
+*Black* prefers double quotes (`"` and `"""`) over single quotes (`'`
+and `'''`).  It will replace the latter with the former as long as it
+does not result in more backslash escapes than before.
+
+*Black* also standardizes string prefixes, making them always lowercase.
+On top of that, if your code is already Python 3.6+ only or it's using
+the `unicode_literals` future import, *Black* will remove `u` from the
+string prefix as it is meaningless in those scenarios.
+
+The main reason to standardize on a single form of quotes is aesthetics.
+Having one kind of quotes everywhere reduces reader distraction.
+It will also enable a future version of *Black* to merge consecutive
+string literals that ended up on the same line (see
+[#26](https://github.com/ambv/black/issues/26) for details).
+
+Why settle on double quotes?  They anticipate apostrophes in English
+text.  They match the docstring standard described in PEP 257.  An
+empty string in double quotes (`""`) is impossible to confuse with
+a one double-quote regardless of fonts and syntax highlighting used.
+On top of this, double quotes for strings are consistent with C which
+Python interacts a lot with.
+
+On certain keyboard layouts like US English, typing single quotes is
+a bit easier than double quotes.  The latter requires use of the Shift
+key.  My recommendation here is to keep using whatever is faster to type
+and let *Black* handle the transformation.
+
+
+### Line breaks & binary operators
+
+*Black* will break a line before a binary operator when splitting a block
+of code over multiple lines. This is so that *Black* is compliant with the
+recent changes in the [PEP 8](https://www.python.org/dev/peps/pep-0008/#should-a-line-break-before-or-after-a-binary-operator)
+style guide, which emphasizes that this approach improves readability.
+
+This behaviour may raise ``W503 line break before binary operator`` warnings in
+style guide enforcement tools like Flake8. Since ``W503`` is not PEP 8 compliant,
+you should tell Flake8 to ignore these warnings.
+
+
+### Slices
+
+PEP 8 [recommends](https://www.python.org/dev/peps/pep-0008/#whitespace-in-expressions-and-statements)
+to treat ``:`` in slices as a binary operator with the lowest priority, and to
+leave an equal amount of space on either side, except if a parameter is omitted
+(e.g. ``ham[1 + 1 :]``). It also states that for extended slices, both ``:``
+operators have to have the same amount of spacing, except if a parameter is
+omitted (``ham[1 + 1 ::]``). *Black* enforces these rules consistently.
+
+This behaviour may raise ``E203 whitespace before ':'`` warnings in style guide
+enforcement tools like Flake8. Since ``E203`` is not PEP 8 compliant, you should
+tell Flake8 to ignore these warnings.
+
+
+### Parentheses
+
+Some parentheses are optional in the Python grammar.  Any expression can
+be wrapped in a pair of parentheses to form an atom.  There are a few
+interesting cases:
+
+- `if (...):`
+- `while (...):`
+- `for (...) in (...):`
+- `assert (...), (...)`
+- `from X import (...)`
+- 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:
+```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

 
 

-There is currently no integration with any text editors. Vim and
-Atom/Nuclide integration is planned by the author, others will require
-external contributions.
+PEP 484 describes the syntax for type hints in Python.  One of the
+use cases for typing is providing type annotations for modules which
+cannot contain them directly (they might be written in C, or they might
+be third-party, or their implementation may be overly dynamic, and so on).
+
+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]`.
+
+
+## Editor integration
+
+### Emacs
+
+Use [proofit404/blacken](https://github.com/proofit404/blacken).
+
+
+### PyCharm
+
+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 with `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 -> Keymap`.
+
+
+### Vim
+
+Commands and shortcuts:
+
+* `,=` or `:Black` to format the entire file (ranges not supported);
+* `:BlackUpgrade` to upgrade *Black* inside the virtualenv;
+* `:BlackVersion` to get the current version of *Black* inside the
+  virtualenv.
+
+Configuration:
+* `g:black_fast` (defaults to `0`)
+* `g:black_linelength` (defaults to `88`)
+* `g:black_virtualenv` (defaults to `~/.vim/black`)
+
+To install with [vim-plug](https://github.com/junegunn/vim-plug):
+
+```
+Plug 'ambv/black',
+```
+
+or with [Vundle](https://github.com/VundleVim/Vundle.vim):
+
+```
+Plugin 'ambv/black'
+```
+
+or you can copy the plugin from [plugin/black.vim](https://github.com/ambv/black/tree/master/plugin/black.vim).
+Let me know if this requires any changes to work with Vim 8's builtin
+`packadd`, or Pathogen, and so on.
+
+This plugin **requires Vim 7.0+ built with Python 3.6+ support**.  It
+needs Python 3.6 to be able to run *Black* inside the Vim process which
+is much faster than calling an external command.
+
+On first run, the plugin creates its own virtualenv using the right
+Python version and automatically installs *Black*. You can upgrade it later
+by calling `:BlackUpgrade` and restarting Vim.
+
+If you need to do anything special to make your virtualenv work and
+install *Black* (for example you want to run a version from master),
+create a virtualenv manually and point `g:black_virtualenv` to it.
+The plugin will use it.
+
+To run *Black* on save, add the following line to `.vimrc` or `init.vim`:
+
+```
+autocmd BufWritePost *.py execute ':Black'
+```
+
+**How to get Vim with Python 3.6?**
+On Ubuntu 17.10 Vim comes with Python 3.6 by default.
+On macOS with Homebrew run: `brew install vim --with-python3`.
+When building Vim from source, use:
+`./configure --enable-python3interp=yes`. There's many guides online how
+to do this.
+
+
+### Visual Studio Code
+
+Use [joslarson.black-vscode](https://marketplace.visualstudio.com/items?itemName=joslarson.black-vscode).
+
+
+### SublimeText 3
+
+Use [sublack plugin](https://github.com/jgirardet/sublack).
+
+
+### IPython Notebook Magic
+
+Use [blackcellmagic](https://github.com/csurfer/blackcellmagic).
+
+
+### Other editors
+
+Atom/Nuclide integration is planned by the author, others 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.
+
+This can be used for example with PyCharm's [File Watchers](https://www.jetbrains.com/help/pycharm/file-watchers.html).
+
+
+## Version control integration
+
+Use [pre-commit](https://pre-commit.com/). Once you [have it
+installed](https://pre-commit.com/#install), add this to the
+`.pre-commit-config.yaml` in your repository:
+```yaml
+repos:
+-   repo: https://github.com/ambv/black
+    rev: stable
+    hooks:
+    - id: black
+      args: [--line-length=88, --safe]
+      python_version: python3.6
+```
+Then run `pre-commit install` and you're ready to go.
+
+`args` in the above config is optional but shows you how you can change
+the line length if you really need to.  If you're already using Python
+3.7, switch the `python_version` accordingly. Finally, `stable` is a tag
+that is pinned to the latest release on PyPI.  If you'd rather run on
+master, this is also an option.
+
+
+## Ignoring unmodified files
+
+*Black* remembers files it has already formatted, unless the `--diff` flag is used or
+code is passed via standard input. This information is stored per-user. The exact
+location of the file depends on the black version and the system on which black
+is run. The file is non-portable. The standard location on common operating systems
+is:
+
+* Windows: `C:\\Users\<username>\AppData\Local\black\black\Cache\<version>\cache.<line-length>.pickle`
+* macOS: `/Users/<username>/Library/Caches/black/<version>/cache.<line-length>.pickle`
+* Linux: `/home/<username>/.cache/black/<version>/cache.<line-length>.pickle`
+

 
 ## Testimonials
 
 
 ## Testimonials
 


@@ -209,25 +654,15 @@ 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!
 
 

-## Tests
+## Show your style

 
 

-Just run:
+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)

 ```
 ```

-python setup.py test
-```
-
-## This tool requires Python 3.6.0+ to run

 
 

-But you can reformat Python 2 code with it, too.  *Black* is able to parse
-all of the new syntax supported on Python 3.6 but also *effectively all*
-the Python 2 syntax at the same time, as long as you're not using print
-statements.
-
-By making the code exclusively Python 3.6+, I'm able to focus on the
-quality of the formatting and re-use all the nice features of the new
-releases (check out [pathlib](docs.python.org/3/library/pathlib.html) or
-f-strings) instead of wasting cycles on Unicode compatibility, and so on.
+Looks like this: [![Code style: black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/ambv/black)

 
 
 ## License
 
 
 ## License


@@ -235,10 +670,10 @@ f-strings) instead of wasting cycles on Unicode compatibility, and so on.
 MIT
 
 
 MIT
 
 

-## Contributing
+## Contributing to Black

 
 

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

 
 Bug reports and fixes are always welcome!  However, before you suggest a
 new feature or configuration knob, ask yourself why you want it.  If it
 
 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


@@ -248,18 +683,316 @@ 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.
 
 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).
+

 
 ## Change Log
 
 
 ## Change Log
 

+### 18.5b1 (unreleased)
+
+* 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
+
+* `# fmt: off` and `# fmt: on` are implemented (#5)
+
+* automatic detection of deprecated Python 2 forms of print statements
+  and exec statements in the formatted file (#49)
+
+* use proper spaces for complex expressions in default values of typed
+  function arguments (#60)
+
+* only return exit code 1 when --check is used (#50)
+
+* don't remove single trailing commas from square bracket indexing
+  (#59)
+
+* don't omit whitespace if the previous factor leaf wasn't a math
+  operator (#55)
+
+* omit extra space in kwarg unpacking if it's the first argument (#46)
+
+* omit extra space in [Sphinx auto-attribute comments](http://www.sphinx-doc.org/en/stable/ext/autodoc.html#directive-autoattribute)
+  (#68)
+
+
+### 18.3a3
+
+* don't remove single empty lines outside of bracketed expressions
+  (#19)
+
+* added ability to pipe formatting from stdin to stdin (#25)
+
+* restored ability to format code with legacy usage of `async` as
+  a name (#20, #42)
+
+* even better handling of numpy-style array indexing (#33, again)
+
+
+### 18.3a2
+
+* changed positioning of binary operators to occur at beginning of lines
+  instead of at the end, following [a recent change to PEP8](https://github.com/python/peps/commit/c59c4376ad233a62ca4b3a6060c81368bd21e85b)
+  (#21)
+
+* ignore empty bracket pairs while splitting. This avoids very weirdly
+  looking formattings (#34, #35)
+
+* remove a trailing comma if there is a single argument to a call
+
+* if top level functions were separated by a comment, don't put four
+  empty lines after the upper function
+
+* fixed unstable formatting of newlines with imports
+
+* fixed unintentional folding of post scriptum standalone comments
+  into last statement if it was a simple statement (#18, #28)
+
+* fixed missing space in numpy-style array indexing (#33)
+
+* fixed spurious space after star-based unary expressions (#31)
+
+
+### 18.3a1
+
+* added `--check`
+
+* only put trailing commas in function signatures and calls if it's
+  safe to do so. If the file is Python 3.6+ it's always safe, otherwise
+  only safe if there are no `*args` or `**kwargs` used in the signature
+  or call. (#8)
+
+* fixed invalid spacing of dots in relative imports (#6, #13)
+
+* fixed invalid splitting after comma on unpacked variables in for-loops
+  (#23)
+
+* fixed spurious space in parenthesized set expressions (#7)
+
+* fixed spurious space after opening parentheses and in default
+  arguments (#14, #17)
+
+* fixed spurious space after unary operators when the operand was
+  a complex expression (#15)
+
+

 ### 18.3a0
 
 * first published version, Happy 🍰 Day 2018!
 
 * alpha quality
 
 ### 18.3a0
 
 * first published version, Happy 🍰 Day 2018!
 
 * alpha quality
 

-* date-versioned (see: http://calver.org/)
+* 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),
+[Carl Meyer](mailto:carl@oddbird.net),
+[Mika Naylor](mailto:mail@autophagy.io), and
+[Zsolt Dollenstein](mailto:zsol.zsol@gmail.com).
+
+Multiple contributions by:
+* [Anthony Sottile](mailto:asottile@umich.edu)
+* [Artem Malyshev](mailto:proofit404@gmail.com)
+* [Christian Heimes](mailto:christian@python.org)
+* [Daniel M. Capella](mailto:polycitizen@gmail.com)
+* [Eli Treuherz](mailto:eli.treuherz@cgi.com)
+* Hugo van Kemenade
+* [Ivan Katanić](mailto:ivan.katanic@gmail.com)
+* [Jelle Zijlstra](mailto:jelle.zijlstra@gmail.com)
+* [Jonas Obrist](mailto:ojiidotch@gmail.com)
+* [Luka Sterbic](mailto:luka.sterbic@gmail.com)
+* [Miguel Gaiowski](mailto:miggaiowski@gmail.com)
+* [Osaetin Daniel](mailto:osaetindaniel@gmail.com)
+* [Sunil Kapil](mailto:snlkapil@gmail.com)
+* [Vishwas B Sharma](mailto:sharma.vishwas88@gmail.com)
+
+---
+
+*Contents:*
+**[Installation and Usage](#installation-and-usage)** |
+**[The *Black* code style](#the-black-code-style)** |
+**[Editor integration](#editor-integration)** |
+**[Version control integration](#version-control-integration)** |
+**[Ignoring unmodified files](#ignoring-unmodified-files)** |
+**[Testimonials](#testimonials)** |
+**[Show your style](#show-your-style)** |
+**[License](#license)** |
+**[Contributing](#contributing-to-black)** |
+**[Change Log](#change-log)** |
+**[Authors](#authors)**