Return calling class from Link constructor methods

Author: duckontheweb

pystac/link.py

@@ -277,8 +277,8 @@ def clone(self) -> "Link":
             title=self.title,
         )
 
-    @staticmethod
-    def from_dict(d: Dict[str, Any]) -> "Link":
+    @classmethod
+    def from_dict(cls, d: Dict[str, Any]) -> "Link":
         """Deserializes a Link from a dict.
 
         Args:
@@ -297,55 +297,56 @@ def from_dict(d: Dict[str, Any]) -> "Link":
         if any(d):
             properties = d
 
-        return Link(
+        return cls(
             rel=rel,
             target=href,
             media_type=media_type,
             title=title,
             properties=properties,
         )
 
-    @staticmethod
-    def root(c: "Catalog_Type") -> "Link":
+    @classmethod
+    def root(cls, c: "Catalog_Type") -> "Link":
         """Creates a link to a root Catalog or Collection."""
-        return Link(pystac.RelType.ROOT, c, media_type=pystac.MediaType.JSON)
+        return cls(pystac.RelType.ROOT, c, media_type=pystac.MediaType.JSON)
 
-    @staticmethod
-    def parent(c: "Catalog_Type") -> "Link":
+    @classmethod
+    def parent(cls, c: "Catalog_Type") -> "Link":
         """Creates a link to a parent Catalog or Collection."""
-        return Link(pystac.RelType.PARENT, c, media_type=pystac.MediaType.JSON)
+        return cls(pystac.RelType.PARENT, c, media_type=pystac.MediaType.JSON)
 
-    @staticmethod
-    def collection(c: "Collection_Type") -> "Link":
+    @classmethod
+    def collection(cls, c: "Collection_Type") -> "Link":
         """Creates a link to an item's Collection."""
-        return Link(pystac.RelType.COLLECTION, c, media_type=pystac.MediaType.JSON)
+        return cls(pystac.RelType.COLLECTION, c, media_type=pystac.MediaType.JSON)
 
-    @staticmethod
-    def self_href(href: str) -> "Link":
+    @classmethod
+    def self_href(cls, href: str) -> "Link":
         """Creates a self link to a file's location."""
-        return Link(pystac.RelType.SELF, href, media_type=pystac.MediaType.JSON)
+        return cls(pystac.RelType.SELF, href, media_type=pystac.MediaType.JSON)
 
-    @staticmethod
-    def child(c: "Catalog_Type", title: Optional[str] = None) -> "Link":
+    @classmethod
+    def child(cls, c: "Catalog_Type", title: Optional[str] = None) -> "Link":
         """Creates a link to a child Catalog or Collection."""
-        return Link(
+        return cls(
             pystac.RelType.CHILD, c, title=title, media_type=pystac.MediaType.JSON
         )
 
-    @staticmethod
-    def item(item: "Item_Type", title: Optional[str] = None) -> "Link":
+    @classmethod
+    def item(cls, item: "Item_Type", title: Optional[str] = None) -> "Link":
         """Creates a link to an Item."""
-        return Link(
+        return cls(
             pystac.RelType.ITEM, item, title=title, media_type=pystac.MediaType.JSON
         )
 
-    @staticmethod
+    @classmethod
     def canonical(
+        cls,
         item_or_collection: Union["Item_Type", "Collection_Type"],
         title: Optional[str] = None,
     ) -> "Link":
         """Creates a canonical link to an Item or Collection."""
-        return Link(
+        return cls(
             pystac.RelType.CANONICAL,
             item_or_collection,
             title=title,

tests/test_link.py

@@ -135,3 +135,43 @@ def test_canonical_collection(self) -> None:
         link = pystac.Link.canonical(self.collection)
         expected = {"rel": "canonical", "href": None, "type": "application/json"}
         self.assertEqual(expected, link.to_dict())
+
+
+class LinkInheritanceTest(unittest.TestCase):
+    def setUp(self) -> None:
+        self.maxDiff = None
+        self.collection = pystac.Collection(
+            "collection id", "desc", extent=ARBITRARY_EXTENT
+        )
+        self.item = pystac.Item(
+            id="test-item",
+            geometry=None,
+            bbox=None,
+            datetime=TEST_DATETIME,
+            properties={},
+        )
+
+    class CustomLink(pystac.Link):
+        pass
+
+    def test_from_dict(self) -> None:
+        link = self.CustomLink.from_dict(
+            {"rel": "r", "href": "t", "type": "a/b", "title": "t", "c": "d", "1": 2}
+        )
+        self.assertIsInstance(link, self.CustomLink)
+
+    def test_collection(self) -> None:
+        link = self.CustomLink.collection(self.collection)
+        self.assertIsInstance(link, self.CustomLink)
+
+    def test_child(self) -> None:
+        link = self.CustomLink.child(self.collection)
+        self.assertIsInstance(link, self.CustomLink)
+
+    def test_canonical_item(self) -> None:
+        link = self.CustomLink.canonical(self.item)
+        self.assertIsInstance(link, self.CustomLink)
+
+    def test_canonical_collection(self) -> None:
+        link = self.CustomLink.canonical(self.collection)
+        self.assertIsInstance(link, self.CustomLink)