Ensure PlatformDirs is valid superclass type for mypy AND not an abstract class for other checkers (#295)

Co-authored-by: Bernát Gábor <[email protected]>

Author: Avasam

src/platformdirs/__init__.py

@@ -19,18 +19,18 @@
     from pathlib import Path
     from typing import Literal
 
+if sys.platform == "win32":
+    from platformdirs.windows import Windows as _Result
+elif sys.platform == "darwin":
+    from platformdirs.macos import MacOS as _Result
+else:
+    from platformdirs.unix import Unix as _Result
 
-def _set_platform_dir_class() -> type[PlatformDirsABC]:
-    if sys.platform == "win32":
-        from platformdirs.windows import Windows as Result  # noqa: PLC0415
-    elif sys.platform == "darwin":
-        from platformdirs.macos import MacOS as Result  # noqa: PLC0415
-    else:
-        from platformdirs.unix import Unix as Result  # noqa: PLC0415
 
+def _set_platform_dir_class() -> type[PlatformDirsABC]:
     if os.getenv("ANDROID_DATA") == "/data" and os.getenv("ANDROID_ROOT") == "/system":
         if os.getenv("SHELL") or os.getenv("PREFIX"):
-            return Result
+            return _Result
 
         from platformdirs.android import _android_folder  # noqa: PLC0415
 
@@ -39,10 +39,14 @@ def _set_platform_dir_class() -> type[PlatformDirsABC]:
 
             return Android  # return to avoid redefinition of a result
 
-    return Result
+    return _Result
 
 
-PlatformDirs = _set_platform_dir_class()  #: Currently active platform
+if TYPE_CHECKING:
+    # Work around mypy issue: https://github.com/python/mypy/issues/10962
+    PlatformDirs = _Result
+else:
+    PlatformDirs = _set_platform_dir_class()  #: Currently active platform
 AppDirs = PlatformDirs  #: Backwards compatibility with appdirs
 
 

tests/test_android.py

@@ -76,7 +76,7 @@ def test_android_folder_from_jnius(mocker: MockerFixture, monkeypatch: pytest.Mo
 
     _android_folder.cache_clear()
 
-    if PlatformDirs is Android:
+    if PlatformDirs is Android:  # type: ignore[comparison-overlap] # See https://github.com/platformdirs/platformdirs/pull/295
         import jnius  # pragma: no cover # noqa: PLC0415
 
         autoclass = mocker.spy(jnius, "autoclass")  # pragma: no cover

tests/test_api.py

@@ -121,3 +121,12 @@ def test_no_ctypes() -> None:
     import platformdirs  # noqa: PLC0415
 
     assert platformdirs
+
+
+def test_mypy_subclassing() -> None:
+    # Ensure that PlatformDirs / AppDirs is seen as a valid superclass by mypy
+    # This is a static type-checking test to ensure we work around
+    # the following mypy issue: https://github.com/python/mypy/issues/10962
+    class PlatformDirsSubclass(platformdirs.PlatformDirs): ...
+
+    class AppDirsSubclass(platformdirs.AppDirs): ...