Implement #370 for Pointcloud extension

Author: duckontheweb

pystac/extensions/pointcloud.py

@@ -522,15 +522,17 @@ def statistics(self, v: Optional[List[PointcloudStatistic]]) -> None:
     def get_schema_uri(cls) -> str:
         return SCHEMA_URI
 
-    @staticmethod
-    def ext(obj: T) -> "PointcloudExtension[T]":
+    @classmethod
+    def ext(cls, obj: T) -> "PointcloudExtension[T]":
         if isinstance(obj, pystac.Item):
+            cls.validate_has_extension(obj)
             return cast(PointcloudExtension[T], ItemPointcloudExtension(obj))
         elif isinstance(obj, pystac.Asset):
+            cls.validate_has_extension(obj)
             return cast(PointcloudExtension[T], AssetPointcloudExtension(obj))
         else:
             raise pystac.ExtensionTypeError(
-                f"File extension does not apply to type {type(obj)}"
+                f"Pointcloud extension does not apply to type {type(obj)}"
             )
 
 

tests/extensions/test_pointcloud.py

@@ -293,3 +293,21 @@ class RandomObject:
 
         with self.assertRaises(ExtensionTypeError):
             PointcloudExtension.ext(RandomObject())  # type: ignore
+
+    def test_extension_not_implemented(self) -> None:
+        # Should raise exception if Item does not include extension URI
+        plain_item_uri = TestCases.get_path("data-files/item/sample-item.json")
+        item = pystac.Item.from_file(plain_item_uri)
+
+        with self.assertRaises(pystac.ExtensionNotImplemented):
+            _ = PointcloudExtension.ext(item)
+
+        # Should raise exception if owning Item does not include extension URI
+        asset = item.assets["thumbnail"]
+
+        with self.assertRaises(pystac.ExtensionNotImplemented):
+            _ = PointcloudExtension.ext(asset)
+
+        # Should succeed if Asset has no owner
+        ownerless_asset = pystac.Asset.from_dict(asset.to_dict())
+        _ = PointcloudExtension.ext(ownerless_asset)