misc: add black (#58937)

.git-blame-ignore-revs

@@ -1,2 +1,4 @@
 # trivial: apply pyupgrade (#58937)
 caa40e7e771b41bd1d164341a2e7f40689cbe4ba
+# trivial: apply black (#58937)
+3ee72e5336d03526c7ab297a5cf09057a6d5d1c2

.pre-commit-config.yaml

@@ -1,8 +1,13 @@
 # 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']
 -   repo: https://github.com/asottile/pyupgrade
     rev: v2.20.0
     hooks:
     - id: pyupgrade
-      args: ['--keep-percent-format', '--py37-plus']
+      args: ['--keep-percent-format', '--py37-plus']

README.txt

@@ -183,6 +183,14 @@ You can put some configuration in ~/.config/eopayment.init ::
 Code Style
 ==========
 
+black is used to format the code, using thoses parameters:
+
+    black --target-version py35 --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.)
+
+
 pyupgrade is used to automatically upgrade syntax, using those parameters:
 
     pyupgrade --keep-percent-format --py37-plus