initial type checking

.github/workflows/type_check.yml

@@ -0,0 +1,33 @@
+name: Type Check
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  type-check:
+    name: Type Check
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Set up python
+        uses: actions/setup-python@v2
+        with:
+          python-version: '3.x'
+
+      - name: Display python version
+        run: python -c "import sys; print(sys.version)"
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install poetry
+          poetry install
+
+      - name: Type check
+        run: poetry run mypy src

.python-version

@@ -0,0 +1 @@
+3.9.1

pyproject.toml

@@ -32,6 +32,7 @@ python = ">= 2.7"
 future = { version = ">= 0.18.0", python = "~2" }
 
 [tool.poetry.dev-dependencies]
+mypy = { version = ">= 0.910", python = ">= 3.5" }
 
 [build-system]
 requires = ["poetry-core>=1.0.0"]