Add typing to public API

pyproject.toml

@@ -32,3 +32,15 @@ showcontent = false
 directory = "removal"
 name = "Removals and Deprecations"
 showcontent = true
+
+
+[tool.mypy]
+files = "src"
+mypy_path = "src"
+namespace_packages = true
+
+[[tool.mypy.overrides]]
+module = [
+    "shellingham.nt"  # Mypy complains that ctypes has no windll on non-Windows machines
+]
+ignore_errors = true

src/shellingham/__init__.py

@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import importlib
 import os
 
@@ -6,7 +8,15 @@
 __version__ = "1.5.4"
 
 
-def detect_shell(pid=None, max_depth=10):
+__all__ = [
+    "ShellDetectionFailure",
+    "detect_shell",
+]
+
+
+def detect_shell(
+    pid: int | None = None, max_depth: int = 10
+) -> tuple[int, int]:
     name = os.name
     try:
         impl = importlib.import_module(".{}".format(name), __name__)

tox.ini

@@ -1,23 +1,23 @@
 [tox]
-envlist = py37, py38, py39, py310, py311, py312
+envlist = py37, py38, py39, py310, py311, py312, test, typing
 
 [gh-actions]
 python =
-    3.7: py37
-    3.8: py38
-    3.9: py39
-    3.10: py310
-    3.11: py311
-    3.12: py312
+    3.7: py37, test, typing
+    3.8: py38, test
+    3.9: py39, test
+    3.10: py310, test
+    3.11: py311, test
+    3.12: py312, test, typing
 
 [testenv]
 allowlist_externals = pipenv
 commands =
     pipenv install --dev
-
-[testenv:test]
-deps =
     pytest
 
+[testenv:typing]
+deps =
+    mypy
 commands =
-    pytest
+    mypy