flake8-black 0.4.0
flake8 plugin to call black as a code style validator
License: MIT
Requires Python: >=3.9
Keywords: black, formatting, style, flake8

flake8-black
============

.. image:: https://img.shields.io/pypi/v/flake8-black.svg
   :alt: Released on the Python Package Index (PyPI)
   :target: https://pypi.org/project/flake8-black/
.. image:: https://img.shields.io/conda/vn/conda-forge/flake8-black.svg
   :alt: Released on Conda
   :target: https://anaconda.org/conda-forge/flake8-black
.. image:: https://results.pre-commit.ci/badge/github/peterjc/flake8-black/master.svg
   :target: https://results.pre-commit.ci/latest/github/peterjc/flake8-black/master
   :alt: pre-commit.ci status
.. image:: https://img.shields.io/github/actions/workflow/status/peterjc/flake8-black/test.yml?logo=github-actions
   :alt: GitHub workflow status
   :target: https://github.com/peterjc/flake8-black/actions
.. image:: https://img.shields.io/pypi/dm/flake8-black.svg
   :alt: PyPI downloads
   :target: https://pypistats.org/packages/flake8-black
.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
   :alt: Code style: black
   :target: https://github.com/python/black

Introduction
------------

This is an MIT licensed `flake8 <https://github.com/pycqa/flake8>`_ plugin
for validating Python code style with the command line code formatting tool
`black <https://github.com/python/black>`_. It is available to install from
the `Python Package Index (PyPI) <https://pypi.org/project/flake8-black/>`_.

Black, *"The Uncompromising Code Formatter"*, is normally run to edit your
Python code in place to match their coding style, a strict subset of the
`PEP 8 style guide <https://www.python.org/dev/peps/pep-0008/>`_.

The point of this plugin is to be able to run ``black --check ...`` from
within the ``flake8`` plugin ecosystem. You might use this via a ``git``
pre-commit hook, or as part of your continuous integration testing.

If you are using `pre-commit <https://pre-commit.com/>`_ configure it to call
black and/or flake8 directly - you do not need flake8-black at all.

Flake8 Validation codes
-----------------------

Early versions of flake8 assumed a single character prefix for the validation
codes, which became problematic with collisions in the plugin ecosystem. Since
v3.0, flake8 has supported longer prefixes, therefore this plugin uses ``BLK``
as its prefix.

====== =======================================================================
Code   Description (*and notes*)
------ -----------------------------------------------------------------------
BLK100 Black would make changes.
BLK9## Internal error (*various, listed below*):
BLK900 Failed to load file: ...
BLK901 Invalid input.
BLK997 Invalid TOML file: ...
BLK998 Could not access flake8 line length setting (*no longer used*).
BLK999 Unexpected exception.
====== =======================================================================

Note that if your Python code has a syntax error, ``black --check ...`` would
report this as an error. Likewise ``flake8 ...`` will by default report the
syntax error, but importantly it does not seem to then call the plugins, so
you will *not* get an additional ``BLK`` error.


Installation
------------

Python 3.9 or later is required, but ``black`` can be used on Python code
written for older versions of Python.

You can install ``flake8-black`` using ``pip``, which should install ``flake8``
and ``black`` as well if not already present::

    $ pip install flake8-black

Alternatively, if you are using the Anaconda packaging system, the following
command will install the plugin with its dependencies::

    $ conda install -c conda-forge flake8-black

The new validator should be automatically included when using ``flake8`` which
may now report additional validation codes starting with ``BLK`` (as defined
above). For example::

    $ flake8 example.py

You can request only the ``BLK`` codes be shown using::

    $ flake8 --select BLK example.py

Python package management
-------------------------

For large projects especially, you should consider pinning the exact
version of black you want to use as their updates do sometimes introduce
changes which would show up as new ``BLK100`` violations via flake8.

You should be able to specify your black version in your conda or pip
requirements or environment, or using using pipenv or poetry etc.

Configuration
-------------

We assume you are familiar with `flake8 configuration
<http://flake8.pycqa.org/en/latest/user/configuration.html>`_ and
`black configuration
<https://black.readthedocs.io/en/stable/usage_and_configuration/the_basics.html#configuration-via-a-file>`_.

We recommend using the following settings in your ``flake8`` configuration,
for example in your ``.flake8``, ``setup.cfg``, or ``tox.ini`` file::

    [flake8]
    # Recommend matching the black line length (default 88),
    # rather than using the flake8 default of 79:
    max-line-length = 88
    extend-ignore =
        # See https://github.com/PyCQA/pycodestyle/issues/373
        E203,

Note currently ``pycodestyle`` gives false positives on the spaces ``black``
uses for slices, which ``flake8`` reports as ``E203: whitespace before ':'``.
Until `pyflakes issue 373 <https://github.com/PyCQA/pycodestyle/issues/373>`_
is fixed, and ``flake8`` is updated, we suggest disabling this style check.

Separately ``pyproject.toml`` is used for ``black`` configuration - if this
file is found, the plugin will look at the following ``black`` settings:

* ``target_version``
* ``skip_string_normalization``
* ``line_length``

You can specify a particular path for the ``pyproject.toml`` file (e.g.
global development settings) using ``--black-config FILENAME`` at the
command line, or using ``black-config = FILENAME`` in your ``flake8``
configuration file.

Ignoring validation codes
-------------------------

Using the flake8 no-quality-assurance pragma comment is not recommended (e.g.
adding ``# noqa: BLK100`` to the first line black would change). Instead use
the black pragma comments ``# fmt: off`` at the start, and ``# fmt: on`` at
the end, of any region of your code which should not be changed. Or, add
``# fmt: skip`` to single lines. Or, exclude the entire file by name (see
below).

Ignoring files
--------------

The plugin does *NOT* currently consider the ``black`` settings ``include``
and ``exclude``, so if you have certain Python files which you do not use
with ``black`` and have told it to ignore, you will *also* need to tell
``flake8`` to ignore them (e.g. using ``exclude`` or ``per-file-ignores``).


Version History
---------------

======= ============ ===========================================================
Version Release date Changes
------- ------------ -----------------------------------------------------------
v0.4.0  *Pending*    - Now tested on Python 3.9 through 3.13, and black 23.9.1
                       (as before) and black 25.9.0 (current latest).
                     - Support the API change in ``decode_bytes`` in black 25.9.0.
                     - Error ``BLK997`` does not have the bad TOML filename.
v0.3.7  2025-09-19   - Now tested on Python 3.8 though 3.13.
                     - Using ``black.Mode`` class name in place of legacy alias
                       ``black.FileMode`` from beta release era.
                     - Does not work on black 25.9.0 onwards.
v0.3.6  2022-12-13   - Use standard library ``tomllib`` on Python 3.11 onwards,
                       contribution from
                       `Ganden Schaffner <https://github.com/gschaffner>`_.
v0.3.5  2022-11-21   - Fix regression clashing with ``flake8-rst-docstrings``.
v0.3.4  2022-11-17   - Replaces ``setup.py`` with ``pyproject.toml`` for build.
v0.3.3  2022-05-16   - Cope with line-length as string in pyproject.toml config.
v0.3.2  2022-02-25   - Use ``tomli`` library to match black, contribution from
                       `Brian Helba <https://github.com/brianhelba>`_.
                     - Adopted GitHub Actions to replace TravisCI testing.
                     - Python 3.7 or later required.
v0.3.0  2022-02-25   - Requires black v22.1.0 (first non-beta release) or later.
                     - Support options "preview", "skip-magic-trailing-comma"
                       in the black TOML file, contribution from
                       `Ferdy <https://github.com/ferdynice>`_.
v0.2.4  2022-01-30   - Support black v22.1.0 which changed a function call,
                       contribution from
                       `Raffaele Salmaso <https://github.com/rsalmaso>`_.
v0.2.3  2021-07-16   - Made ``toml`` dependency explicit in ``setup.py``.
v0.2.2  2021-07-16   - Declared ``toml`` dependency (for black 21.7b0).
v0.2.1  2020-07-25   - Detect ``*.pyi`` files via extension.
v0.2.0  2020-05-20   - Minimum requirement on black 19.3b0 or later is now
                       implicit. This is a workaround for `pipenv issue 3928
                       <https://github.com/pypa/pipenv/issues/3928>`_. Upgrade
                       black if running flake8 gives an error like this:
                       ``Flake8 failed to load plugin "BLK" due to __call__()
                       got an unexpected keyword argument 'target_versions'.``
v0.1.2  2020-05-18   - Removed test broken by flake8 v3.8 change to resolve
                       configuration files relative to current directory.
v0.1.1  2019-08-26   - Option to use a (global) black configuration file,
                       contribution from
                       `Tomasz Grining <https://github.com/098799>`_.
                     - New ``BLK997`` if can't parse ``pyproject.toml`` file.
                     - Logs configuration files, use ``-v`` or ``--verbose``.
                     - Fixed flake8 "builtins" parameter warning.
                     - Now requires black 19.3b0 or later.
v0.1.0  2019-06-03   - Uses main black settings from ``pyproject.toml``,
                       contribution from `Alex <https://github.com/ADKosm>`_.
                     - WARNING: Now ignores flake8 ``max-line-length`` setting.
v0.0.4  2019-03-15   - Supports black 19.3b0 which changed a function call.
v0.0.3  2019-02-21   - Bug fix when ``W292 no newline at end of file`` applies,
                       contribution from
                       `Sapphire Becker <https://github.com/sapphire-janrain>`_.
v0.0.2  2019-02-15   - Document syntax error behaviour (no BLK error reported).
v0.0.1  2019-01-10   - Initial public release.
                     - Passes flake8 ``max-line-length`` setting to black.
======= ============ ===========================================================


Developers
----------

This plugin is on GitHub at https://github.com/peterjc/flake8-black

Developers may install the plugin from the git repository with optional build
dependencies::

    $ pip install -e .[develop]

To make a new release once tested locally and online::

    $ git tag vX.Y.Z
    $ python -m build
    $ git push origin master --tags
    $ twine upload dist/flake8?black-X.Y.Z*

The PyPI upload should trigger an automated pull request updating the
`flake8-black conda-forge recipe
<https://github.com/conda-forge/flake8-black-feedstock/blob/master/recipe/meta.yaml>`_.