Enable flake8

.github/workflows/flake8.yml

@@ -0,0 +1,33 @@
+name: flake8
+
+on:
+  # Trigger the workflow on push or pull request,
+  # but only for the master branch
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  flake8:
+    runs-on: ubuntu-latest 
+
+    steps:
+    - name: Checkout devito_book
+      uses: actions/checkout@v1
+
+    - name: Set up Python 3.7
+      uses: actions/setup-python@v1
+      with:
+        python-version: 3.7
+
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install flake8
+    - name: Lint with flake8
+      run: |
+        flake8 --builtins=ArgumentError .
+