Filter links with only media_type

CHANGELOG.md

@@ -29,6 +29,7 @@
 - Serializing optional Collection attributes ([#916](https://github.com/stac-utils/pystac/pull/916))
 - A couple non-running tests ([#912](https://github.com/stac-utils/pystac/pull/912))
 - Support relative stac extension paths via `make_absolute_href` ([#884](https://github.com/stac-utils/pystac/pull/884))
+- Filtering on `media_type` in `get_links()` and `get_single_link()` ([#966](https://github.com/stac-utils/pystac/pull/966))
 
 ## [v1.6.1]
 

pystac/stac_object.py

@@ -83,23 +83,30 @@ def remove_links(self, rel: Union[str, pystac.RelType]) -> None:
 
     def get_single_link(
         self,
-        rel: Union[str, pystac.RelType],
+        rel: Optional[Union[str, pystac.RelType]] = None,
         media_type: Optional[Union[str, pystac.MediaType]] = None,
     ) -> Optional[Link]:
-        """Get single link that match the given ``rel`` and, optionally,
-        ``media_type``. If ``media_type`` is ``None``, then the link is
-        matched only on the ``rel`` value.
+        """Get a single :class:`~pystac.Link` instance associated with this
+        object.
 
         Args:
-             rel : The :class:`~pystac.Link` ``rel`` to match on.
-             media_type: The :class:`~pystack.MediaType` ``media_type`` to match on
-        """
+            rel : If set, filter links such that only those
+                matching this relationship are returned.
+            media_type: If set, filter the links such that only
+                those matching media_type are returned
 
+        Returns:
+            Optional[:class:`~pystac.Link`]: First link that matches ``rel``
+                and/or ``media_type``, or else the first link associated with
+                this object.
+        """
+        if rel is None and media_type is None:
+            return next(iter(self.links), None)
         return next(
             (
                 link
                 for link in self.links
-                if link.rel == rel
+                if (rel is None or link.rel == rel)
                 and (media_type is None or link.media_type == media_type)
             ),
             None,
@@ -119,16 +126,17 @@ def get_links(
                 those matching media_type are returned
 
         Returns:
-            List[:class:`~pystac.Link`]: A list of links that match ``rel`` if set,
-                or else all links associated with this object.
+            List[:class:`~pystac.Link`]: A list of links that match ``rel`` and/
+                or ``media_type`` if set, or else all links associated with this
+                object.
         """
-        if rel is None:
+        if rel is None and media_type is None:
             return self.links
         else:
             return [
                 link
                 for link in self.links
-                if link.rel == rel
+                if (rel is None or link.rel == rel)
                 and (media_type is None or link.media_type == media_type)
             ]
 

tests/test_catalog.py

@@ -1238,14 +1238,24 @@ def test_get_single_links_media_type(self) -> None:
             )
         )
 
-        html_link = catalog.get_single_link("search")
+        html_link = catalog.get_single_link(rel="search")
         assert html_link is not None
         assert html_link.href == "./search.html"
-        json_link = catalog.get_single_link("search", media_type="application/geo+json")
+        html_link = catalog.get_single_link(media_type="text/html")
+        assert html_link is not None
+        assert html_link.href == "./search.html"
+        json_link = catalog.get_single_link(
+            rel="search", media_type="application/geo+json"
+        )
         assert json_link is not None
         assert json_link.href == "./search.json"
+        no_link = catalog.get_single_link(rel="via")
+        assert no_link is None
+        first_link = catalog.get_single_link()
+        assert first_link is not None
+        assert first_link.rel == "self"
 
-    def test_get_links_media_type(self) -> None:
+    def test_get_links(self) -> None:
         catalog = TestCases.case_1()
 
         catalog.links.append(
@@ -1256,7 +1266,13 @@ def test_get_links_media_type(self) -> None:
                 rel="search", target="./search.json", media_type="application/geo+json"
             )
         )
-        assert len(catalog.get_links("search", media_type="application/geo+json")) == 1
+        assert (
+            len(catalog.get_links(rel="search", media_type="application/geo+json")) == 1
+        )
+        assert len(catalog.get_links(media_type="text/html")) == 1
+        assert len(catalog.get_links(rel="search")) == 2
+        assert len(catalog.get_links(rel="via")) == 0
+        assert len(catalog.get_links()) == 6
 
     def test_to_dict_no_self_href(self) -> None:
         catalog = Catalog(id="an-id", description="A test Catalog")