misc: add black files/notes (#51575)

.git-blame-ignore-revs

@@ -0,0 +1 @@
+5b9bc1ff57cfb47458d629c15bcae28ae0bc141b

.pre-commit-config.yaml

@@ -0,0 +1,8 @@
+# See https://pre-commit.com for more information
+# See https://pre-commit.com/hooks.html for more hooks
+repos:
+-   repo: https://github.com/psf/black
+    rev: 20.8b1
+    hooks:
+    - id: black
+      args: ['--target-version', 'py37', '--skip-string-normalization', '--line-length', '110']

README

@@ -318,6 +318,16 @@ Unit tests are written using pytest and launched using tox, and can be run with:
 
    tox
 
+Code Style
+----------
+
+black is used to format the code, using thoses parameters:
+
+    black --target-version py37 --skip-string-normalization --line-length 110
+
+There is .pre-commit-config.yaml to use pre-commit to automatically run black
+before commits. (execute `pre-commit install` to install the git hook.)
+
 Remarks
 =======
 

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = coverage-py2-dj111-{pg,sqlite},coverage-py3-dj{111,22}-{pg,sqlite}
+envlist = black,coverage-py2-dj111-{pg,sqlite},coverage-py3-dj{111,22}-{pg,sqlite}
 toxworkdir = {env:TMPDIR:/tmp}/tox-{env:USER}/django-mellon/
 
 [testenv]
@@ -59,6 +59,12 @@ commands =
   ./getlasso3.sh
   django-admin {posargs:--help}
 
+[testenv:black]
+skip_install = true
+deps =
+  pre-commit
+commands =
+  pre-commit run black --all-files --show-diff-on-failure
 
 [pytest]
 junit_family=legacy