add a flake8 job

.github/workflows/main.yml

@@ -11,6 +11,26 @@ on:
   workflow_dispatch:
 
 jobs:
+  flake8:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Set up Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: '3.9'
+
+      - name: Install dependencies
+        run: |
+          python3 -m pip install --upgrade pip
+          python3 -m pip install flake8
+      - name: Lint with flake8
+        run: |
+          # stop the build if there are Python syntax errors or undefined names
+          flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
+          # use flake8 to check formatting, based on example here https://black.readthedocs.io/en/stable/the_black_code_style/current_style.html
+          flake8 . --count --select=C,E,F,W,B,B950 --max-complexity=10 --max-line-length=88 --statistics --extend-ignore=E203
   build:
     runs-on: ubuntu-latest
     strategy: