Black

.github/PULL_REQUEST_TEMPLATE.md

@@ -2,4 +2,5 @@
 
  - [ ] Closes #xxxx
  - [ ] Tests added
+ - [ ] Passes `black .` & `flake8`
  - [ ] Fully documented, including `whats-new.rst` for all changes and `api.rst` for new API

.pre-commit-config.yaml

@@ -0,0 +1,12 @@
+# https://pre-commit.com/
+# https://github.com/python/black#version-control-integration
+repos:
+  - repo: https://github.com/python/black
+    rev: stable
+    hooks:
+      - id: black
+        language_version: python3.7
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v2.2.3
+    hooks:
+      - id: flake8

README.rst

@@ -11,6 +11,9 @@ xarray: N-D labeled arrays and datasets
   :target: https://pandas.pydata.org/speed/xarray/
 .. image:: https://img.shields.io/pypi/v/xarray.svg
    :target: https://pypi.python.org/pypi/xarray/
+.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
+    :target: https://github.com/python/black
+
 
 **xarray** (formerly **xray**) is an open source project and Python package
 that makes working with labelled multi-dimensional arrays simple,

azure-pipelines.yml

@@ -55,6 +55,10 @@ jobs:
     displayName: Install flake8
   - bash: flake8
     displayName: flake8 lint checks
+  - bash: python -m pip install black
+    displayName: Install black
+  - bash: black .
+    displayName: black formatting check
 
 - job: TypeChecking
   variables:

doc/contributing.rst

@@ -340,23 +340,24 @@ do not make sudden changes to the code that could have the potential to break
 a lot of user code as a result, that is, we need it to be as *backwards compatible*
 as possible to avoid mass breakages.
 
-Python (PEP8)
-~~~~~~~~~~~~~
+Code Formatting
+~~~~~~~~~~~~~~~
 
-*xarray* uses the `PEP8 <http://www.python.org/dev/peps/pep-0008/>`_ standard.
-There are several tools to ensure you abide by this standard. Here are *some* of
-the more common ``PEP8`` issues:
+Xarray uses `Black <https://black.readthedocs.io/en/stable/>`_ and
+`Flake8 <http://flake8.pycqa.org/en/latest/>`_ to ensure a consistent code
+format throughout the project. ``black`` and ``flake8`` can be installed with
+``pip``::
 
-  - we restrict line-length to 79 characters to promote readability
-  - passing arguments should have spaces after commas, e.g. ``foo(arg1, arg2, kw1='bar')``
+   pip install black flake8
 
-:ref:`Continuous Integration <contributing.ci>` will run
-the `flake8 <http://flake8.pycqa.org/en/latest/>`_ tool
-and report any stylistic errors in your code. Therefore, it is helpful before
-submitting code to run the check yourself:
+and then run from the root of the Xarray repository::
 
+   black .
    flake8
 
+to auto-format your code. Additionally, many editors have plugins that will
+apply ``black`` as you edit files.
+
 Other recommended but optional tools for checking code quality (not currently
 enforced in CI):
 
@@ -367,8 +368,20 @@ enforced in CI):
   incorrectly sorted imports. ``isort -y`` will automatically fix them. See
   also `flake8-isort <https://github.com/gforcada/flake8-isort>`_.
 
-Note that your code editor probably supports extensions that can show results
-of these checks inline as you type.
+Optionally, you may wish to setup `pre-commit hooks <https://pre-commit.com/>`_
+to automatically run ``black`` and ``flake8`` when you make a git commit. This
+can be done by installing ``pre-commit``::
+
+   pip install pre-commit
+
+and then running::
+
+   pre-commit install
+
+from the root of the Xarray repository. Now ``black`` and ``flake8`` will be run
+each time you commit changes. You can skip these checks with
+``git commit --no-verify``.
+
 
 Backwards Compatibility
 ~~~~~~~~~~~~~~~~~~~~~~~