Use black through pre-commit, and enforce it in CI

* [CI] Add job 'Format'
* add dev-requirements.txt
* add .pre-commit-config.yaml

.github/workflows/ci.yml

@@ -12,7 +12,23 @@ on:
 
 jobs:
 
-  build:
+  Format:
+    name: 🐍 Format
+    runs-on: ubuntu-latest
+    steps:
+
+    - name: 🧰 Checkout
+      uses: actions/checkout@v2
+
+    - name: 🐍 Setup Python ${{ matrix.pyver }}
+      uses: actions/setup-python@v2
+      with:
+        python-version: '3.10'
+
+    - name: 🚦 Run pre-commit Action
+      uses: pre-commit/[email protected]
+
+  Build:
     strategy:
       fail-fast: false
       matrix:

.pre-commit-config.yaml

@@ -0,0 +1,7 @@
+# Configuration for pre-commit (https://pre-commit.com/), a tool to run
+# formatters, linters, and other productivity tools before a commit.
+repos:
+  - repo: https://github.com/psf/black
+    rev: 21.7b0
+    hooks:
+      - id: black

dev-requirements.txt

@@ -0,0 +1,2 @@
+pre-commit>=2.9.0
+tox