Add a function to parse an Item from its canonical URI

SPARQL results seem to be in this form.

rock_paper_sand/wikidata_value.py

@@ -85,6 +85,13 @@ def uri(self) -> str:
         """
         return f"{_ITEM_PREFIX_CANONICAL_URI}{self.id}"
 
+    @classmethod
+    def from_uri(cls, value: str) -> Self:
+        """Returns the item parsed from its canonical URI."""
+        return cls(
+            _parse_id(value, prefixes=(_ITEM_PREFIX_CANONICAL_URI,), letter="Q")
+        )
+
 
 _i = Item.from_string
 Q_GREGORIAN_CALENDAR = _i("https://www.wikidata.org/wiki/Q12138")

rock_paper_sand/wikidata_value_test.py

@@ -55,6 +55,18 @@ def test_item_uri(self) -> None:
             wikidata_value.Item("Q1").uri,
         )
 
+    def test_item_from_uri_invalid(self) -> None:
+        with self.assertRaisesRegex(ValueError, "Wikidata IRI or ID"):
+            wikidata_value.Item.from_uri("Q1")
+
+    def test_item_from_uri_valid(self) -> None:
+        self.assertEqual(
+            "Q1",
+            wikidata_value.Item.from_uri(
+                "http://www.wikidata.org/entity/Q1"
+            ).id,
+        )
+
     def test_invalid_property_id(self) -> None:
         with self.assertRaisesRegex(ValueError, "Wikidata IRI or ID"):
             wikidata_value.Property("foo")