Add GitHub action to lint python code. Only takes a minute or

two, so it's good to have "always on" in production and custom
branches. Just for comparison, also run -1 version (3.7) and +1
version (3.9).

.github/workflows/python-lint.yml

@@ -0,0 +1,63 @@
+# This is a basic workflow to help you get started with Actions
+
+name: Lint all Python code
+
+# Triggers the workflow on push or pull request events
+on:
+  push:
+  pull_request:
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+jobs:
+  # This workflow contains a single job called "pylint"
+  pylint:
+    runs-on: ubuntu-latest
+    continue-on-error: ${{ matrix.experimental }}
+    # The type of runner that the job will run on
+    env:
+      PYTHON_CMD: "python${{ matrix.python-version }}"
+      PLARGS: "${{ matrix.extra_args }}"
+
+    strategy:
+      matrix:
+        python-version: ['3.8']
+        experimental: [false]
+        extra_args: ['']
+        include:
+          - python-version: '3.7'
+            experimental: true
+            extra_args: "--disable=not-context-manager"
+          - python-version: '3.9'
+            experimental: true
+            extra_args: "--disable=unsubscriptable-object,inherit-non-class"
+
+    # Steps represent a sequence of tasks that will be executed as part of the job
+    steps:
+      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v2
+
+      - name: Checkout submodules
+        run: git submodule update --init --recursive
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install dependencies
+        run: |
+          ${PYTHON_CMD} -m pip install --upgrade pip
+          ${PYTHON_CMD} -m pip install wheel pylint
+          sudo apt install -y libcurl4-openssl-dev
+          ${PYTHON_CMD} -m pip install numpy sympy psutil raven setproctitle cffi \
+           json-rpc websocket-client nose hexdump matplotlib crcmod tqdm requests \
+           zmq logentries PyJWT scipy libusb1 SCons Cython jinja2 atomicwrites \
+           pyserial pyyaml pycapnp smbus2 parameterized pycurl azure-storage-blob==2.1.0 \
+           dictdiffer
+
+      - name: script
+        run: |
+          pylint --extension-pkg-whitelist=zmq -j 0 -E --reports=y ${PLARGS} `find ./ -name \*.py | grep -v '^[.]/external' | \
+           sed 's|[.]/||;s|/.*||' | sort -u`