enable mypy type checking

.github/workflows/ci.yml

@@ -36,13 +36,17 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install flake8 pytest pytest-mock
+          pip install flake8 pytest pytest-mock mypy types-protobuf
           pip install --use-pep517 -r requirements.txt
+          mypy --install-types --non-interactive
       - 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
           # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
           flake8 . --count --exit-zero --max-complexity=10 --max-line-length=200 --statistics
+      - name: Type checking with mypy
+        run: |
+          mypy *.py
       - name: Test with pytest
         run: pytest