Use ABCMeta in classes with abstractmethod

src/PIL/BlpImagePlugin.py

@@ -291,7 +291,7 @@ def _open(self) -> None:
         self.tile = [ImageFile._Tile(decoder, (0, 0) + self.size, offset, args)]
 
 
-class _BLPBaseDecoder(ImageFile.PyDecoder):
+class _BLPBaseDecoder(abc.ABC, ImageFile.PyDecoder):
     _pulls_fd = True
 
     def decode(self, buffer: bytes | Image.SupportsArrayInterface) -> tuple[int, int]:

src/PIL/Image.py

@@ -2966,7 +2966,7 @@ def toqpixmap(self) -> ImageQt.QPixmap:
 # Abstract handlers.
 
 
-class ImagePointHandler:
+class ImagePointHandler(abc.ABC):
     """
     Used as a mixin by point transforms
     (for use with :py:meth:`~PIL.Image.Image.point`)
@@ -2977,7 +2977,7 @@ def point(self, im: Image) -> Image:
         pass
 
 
-class ImageTransformHandler:
+class ImageTransformHandler(abc.ABC):
     """
     Used as a mixin by geometry transforms
     (for use with :py:meth:`~PIL.Image.Image.transform`)

src/PIL/ImageFile.py

@@ -438,7 +438,7 @@ def _seek_check(self, frame: int) -> bool:
         return self.tell() != frame
 
 
-class StubHandler:
+class StubHandler(abc.ABC):
     def open(self, im: StubImageFile) -> None:
         pass
 
@@ -447,17 +447,17 @@ def load(self, im: StubImageFile) -> Image.Image:
         pass
 
 
-class StubImageFile(ImageFile):
+class StubImageFile(ImageFile, metaclass=abc.ABCMeta):
     """
     Base class for stub image loaders.
 
     A stub loader is an image loader that can identify files of a
     certain format, but relies on external code to load the file.
     """
 
+    @abc.abstractmethod
     def _open(self) -> None:
-        msg = "StubImageFile subclass must implement _open"
-        raise NotImplementedError(msg)
+        pass
 
     def load(self) -> Image.core.PixelAccess | None:
         loader = self._load()
@@ -471,10 +471,10 @@ def load(self) -> Image.core.PixelAccess | None:
         self.__dict__ = image.__dict__
         return image.load()
 
+    @abc.abstractmethod
     def _load(self) -> StubHandler | None:
         """(Hook) Find actual image loader."""
-        msg = "StubImageFile subclass must implement _load"
-        raise NotImplementedError(msg)
+        pass
 
 
 class Parser:

src/PIL/ImageFilter.py

@@ -27,7 +27,7 @@
     from ._typing import NumpyArray
 
 
-class Filter:
+class Filter(abc.ABC):
     @abc.abstractmethod
     def filter(self, image: _imaging.ImagingCore) -> _imaging.ImagingCore:
         pass

src/PIL/ImageShow.py

@@ -192,7 +192,7 @@ def show_file(self, path: str, **options: Any) -> int:
     register(MacViewer)
 
 
-class UnixViewer(Viewer):
+class UnixViewer(abc.ABC, Viewer):
     format = "PNG"
     options = {"compress_level": 1, "save_all": True}