Add type-checking infrastructure

Run mypy during pre-commit.  For now, only type-check setup.py and
_version.py.

We will support type checking on Python >= 3.10.  3.9 has too many
limitations to be worth supporting.

Signed-off-by: Benjamin Gilbert <bgilbert@cs.cmu.edu>

Author: bgilbert

.pre-commit-config.yaml

@@ -53,6 +53,14 @@ repos:
         name: Lint python code with flake8
         additional_dependencies: [flake8-bugbear, Flake8-pyproject]
 
+  - repo: https://github.com/pre-commit/mirrors-mypy
+    rev: v1.11.2
+    hooks:
+      - id: mypy
+        name: Check Python types
+        additional_dependencies: [types-setuptools]
+        exclude: "^(doc/.*|openslide/(__init__|deepzoom|lowlevel)\\.py|tests/.*|examples/deepzoom/.*)$"
+
   - repo: https://github.com/rstcheck/rstcheck
     rev: v6.2.4
     hooks:

pyproject.toml

@@ -57,6 +57,12 @@ extend-ignore = ["E203", "E741"]
 profile = "black"
 force_sort_within_sections = true
 
+[tool.mypy]
+python_version = "3.10"
+strict = true
+# temporary, while we bootstrap type checking
+follow_imports = "silent"
+
 [tool.pytest.ini_options]
 minversion = "7.0"
 # don't try to import openslide from the source directory, since it doesn't