pyflakes (#3266)

.github/workflows/lint_python.yaml

@@ -0,0 +1,12 @@
+name: lint_python
+on: [push, pull_request] 
+jobs:
+  lint_python:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions/setup-python@v1
+        with:
+          python_version: "3.8"
+      - run: "python -m pip install flake8"
+      - run: "python -m flake8 . --count --select=E9,F7,F82 --show-source"