Add keywords to common metadata (#1443)

* add keywords to common metadata

* Update pystac/common_metadata.py

* fix: lint

---------

Co-authored-by: Pete Gadomski <pete.gadomski@gmail.com>

Author: tylanderson

CHANGELOG.md

@@ -13,6 +13,7 @@
 - Add netCDF to pystac.media_type ([#1386](https://github.com/stac-utils/pystac/pull/1386))
 - Add convenience method for accessing pystac_client ([#1365](https://github.com/stac-utils/pystac/pull/1365))
 - Fix field ordering when saving `Item`s ([#1423](https://github.com/stac-utils/pystac/pull/1423))
+- Add keywords to common metadata ([#1443](https://github.com/stac-utils/pystac/pull/1443))
 - Add roles to common metadata ([#1444](https://github.com/stac-utils/pystac/pull/1444/files))
 
 ### Changed

pystac/common_metadata.py

@@ -232,6 +232,15 @@ def updated(self) -> datetime | None:
     def updated(self, v: datetime | None) -> None:
         self._set_field("updated", utils.map_opt(utils.datetime_to_str, v))
 
+    @property
+    def keywords(self) -> list[str] | None:
+        """Get or set the keywords describing the STAC entity."""
+        return self._get_field("keywords", list[str])
+
+    @keywords.setter
+    def keywords(self, v: list[str] | None) -> None:
+        self._set_field("keywords", v)
+
     @property
     def roles(self) -> list[str] | None:
         """Get or set the semantic roles of the entity."""

tests/data-files/item/sample-item-asset-properties.json

@@ -74,6 +74,7 @@
       "start_datetime": "2017-05-01T13:22:30.040Z",
       "end_datetime": "2017-05-02T13:22:30.040Z",
       "license": "CC-BY-4.0",
+      "keywords": ["keyword_a"],
       "roles": ["a_role"],
       "providers": [
         {

tests/test_common_metadata.py

@@ -541,6 +541,28 @@ def test_updated(self) -> None:
             analytic.to_dict()["updated"], utils.datetime_to_str(set_value)
         )
 
+    def test_keywords(self) -> None:
+        item = self.item.clone()
+        cm = item.common_metadata
+        analytic = item.assets["analytic"]
+        analytic_cm = CommonMetadata(analytic)
+        thumbnail = item.assets["thumbnail"]
+        thumbnail_cm = CommonMetadata(thumbnail)
+
+        item_value = cm.keywords
+        a2_known_value = ["keyword_a"]
+
+        # Get
+        self.assertNotEqual(thumbnail_cm.keywords, item_value)
+        self.assertEqual(thumbnail_cm.keywords, a2_known_value)
+
+        # Set
+        set_value = ["keyword_b"]
+        analytic_cm.keywords = set_value
+
+        self.assertEqual(analytic_cm.keywords, set_value)
+        self.assertEqual(analytic.to_dict()["keywords"], set_value)
+
     def test_roles(self) -> None:
         item = self.item.clone()
         cm = item.common_metadata