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The uncompromising code formatter.

Project description

black
=====

|Build Status|

Any color you like.

*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.

*Black* makes code review faster by producing the smallest diffs
possible.

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``.

Usage
-----

*Black* can be installed by running ``pip install black``.

::

black [OPTIONS] [SRC]...

Options:
-l, --line-length INTEGER Where to wrap around. [default: 88]
--fast / --safe If --fast given, skip temporary sanity checks.
[default: --safe]
--version Show the version and exit.
--help Show this message and exit.

The philosophy behind *Black*
-----------------------------

*Black* reformats entire files in place. It is not configurable. It
doesn’t take previous formatting into account. It doesn’t reformat
blocks that start with ``# fmt: off`` and end with ``# fmt: on``. It
also recognizes `YAPF <https://github.com/google/yapf>`__\ ’s block
comments to the same effect, as a courtesy for straddling code.

How *Black* formats files
~~~~~~~~~~~~~~~~~~~~~~~~~

*Black* ignores previous formatting and applies uniform horizontal and
vertical whitespace to your code. The rules for horizontal whitespace
are pretty obvious and can be summarized as: do whatever makes
``pycodestyle`` happy.

As for vertical whitespace, *Black* tries to render one full expression
or simple statement per line. If this fits the allotted line length,
great.

.. code:: !py3

# in:
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.

.. code:: !py3

# in:
l = [[n for n in list_bosses()], [n for n in list_employees()]]

# out:
l = [
[n for n in list_bosses()], [n for n in list_employees()]
]

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.

.. code:: !py3

# in:
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:
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:
...

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).

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

*Black* avoids spurious vertical whitespace. This is in the spirit of
PEP 8 which says that in-function vertical whitespace should only be
used sparingly. One exception is control flow statements: *Black* will
always emit an extra empty line after ``return``, ``raise``, ``break``,
``continue``, and ``yield``. This is to make changes in control flow
more prominent to readers of your code.

That’s it. The rest of the whitespace formatting rules follow PEP 8 and
are designed to keep ``pycodestyle`` quiet.

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:

.. code:: !ini

[flake8]
max-line-length = 80
...
select = C,E,F,W,B,B950
ignore = E501

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”.

Editor integration
~~~~~~~~~~~~~~~~~~

There is currently no integration with any text editors. Vim and
Atom/Nuclide integration is planned by the author, others will require
external contributions.

Patches welcome! ✨ 🍰 ✨

Testimonials
------------

**Dusty Phillips**,
`writer <https://smile.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=dusty+phillips>`__:

Black is opinionated so you don’t have to be.

**Hynek Schlawack**, `creator of ``attrs`` <http://www.attrs.org/>`__,
core developer of Twisted and CPython:

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

**Carl Meyer**, `Django <https://www.djangoproject.com/>`__ core
developer:

At least the name is good.

Tests
-----

Just run:

::

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.

License
-------

MIT

Contributing
------------

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

Change Log
----------

18.3a0
~~~~~~

- first published version, Happy 🍰 Day 2018!

- alpha quality

- date-versioned (see: http://calver.org/)

Authors
-------

Glued together by `Łukasz Langa <mailto:lukasz@langa.pl>`__.

.. |Build Status| image:: https://travis-ci.org/ambv/black.svg?branch=master
:target: https://travis-ci.org/ambv/black


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