🚧 Add Type Checking using mypy (#723)

- Add type checking using `mypy`, a static type checker for Python.

- A GitHub action has been created to run `mypy` after push and pull requests.
- Currently, only `tiatoolbox/__init__.py` has been checked to work without errors with `mypy`.

---------

Co-authored-by: Shan E Ahmed Raza <[email protected]>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: 3 people

.github/workflows/mypy-type-check.yml

@@ -0,0 +1,37 @@
+# This workflow will perform code type checking using mypy
+
+name: mypy type checking
+
+on:
+  push:
+    branches: [ develop, pre-release, master, main ]
+  pull_request:
+    branches: [ develop, pre-release, master, main ]
+
+jobs:
+
+  build:
+
+    runs-on: ubuntu-22.04
+
+    strategy:
+      matrix:
+        python-version: ["3.8", "3.9", "3.10", "3.11"]
+
+    steps:
+
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v3
+      with:
+        python-version: ${{ matrix.python-version }}
+
+    - name: Checkout repository
+      uses: actions/checkout@v3
+
+    - name: Setup mypy
+      run: |
+        pip install mypy
+
+    - name: Perform type checking
+      run: |
+        mypy --install-types --non-interactive --follow-imports=skip tiatoolbox/__init__.py

tests/test_init.py

@@ -139,3 +139,14 @@ def test_lazy_import() -> None:
     )
 
     assert "exceptions" in sys.modules
+
+
+def test_lazy_import_module_not_found() -> None:
+    """'Test lazy import for ModuleNotFoundError."""
+    from tiatoolbox import _lazy_import
+
+    with pytest.raises(ModuleNotFoundError):
+        _lazy_import(
+            "nonexistent_module",
+            Path(__file__).parent.parent / "tiatoolbox",
+        )

tiatoolbox/__init__.py

@@ -9,12 +9,14 @@
 if sys.version_info >= (3, 9):  # pragma: no cover
     import importlib.resources as importlib_resources
 else:  # pragma: no cover
-    import importlib_resources  # To support Python 3.8
+    # To support Python 3.8
+    import importlib_resources  # type: ignore[import-not-found]
 
 import yaml
 
 if TYPE_CHECKING:  # pragma: no cover
     from logging import LogRecord
+    from types import ModuleType
 
 __author__ = """TIA Centre"""
 __email__ = "[email protected]"
@@ -71,6 +73,7 @@ def filter(self: DuplicateFilter, record: LogRecord) -> bool:
 
 
 # runtime context parameters
+rcParam: dict[str, str | Path | dict]  # noqa: N816
 rcParam = {  # noqa: N816
     "TIATOOLBOX_HOME": Path.home() / ".tiatoolbox",
 }
@@ -88,6 +91,7 @@ def read_registry_files(path_to_registry: str | Path) -> dict | str:
 
 
     """
+    path_to_registry = str(path_to_registry)  # To pass tests with Python 3.8
     pretrained_files_registry_path = importlib_resources.as_file(
         importlib_resources.files("tiatoolbox") / path_to_registry,
     )
@@ -101,8 +105,10 @@ def read_registry_files(path_to_registry: str | Path) -> dict | str:
 rcParam["pretrained_model_info"] = read_registry_files("data/pretrained_model.yaml")
 
 
-def _lazy_import(name: str, module_location: Path) -> sys.modules:
+def _lazy_import(name: str, module_location: Path) -> ModuleType:
     spec = importlib.util.spec_from_file_location(name, module_location)
+    if spec is None or spec.loader is None:
+        raise ModuleNotFoundError(name=name, path=str(module_location))
     loader = importlib.util.LazyLoader(spec.loader)
     spec.loader = loader
     module = importlib.util.module_from_spec(spec)