Allow rest sensor list responses (#28835)

* Make rest sensor a little bit more flexible and allow the response to be a list with 0th element being a dictionary

* Black formatter wanted a different formatting

* Added test case for a list response with dict as 0th element

* Fixed lint error - it thinks a + STRING is an avoidance of using % sequences for log messages; I generally prefer explicit + rather than string juxtaposition for combining string literals, but sounds like that's not the standard

* Fixed test case -- I added it to the wrong scenario and need to use the one with json_attrs.

homeassistant/components/rest/sensor.py

@@ -197,13 +197,18 @@ class RestSensor(Entity):
             if value:
                 try:
                     json_dict = json.loads(value)
+                    if isinstance(json_dict, list):
+                        json_dict = json_dict[0]
                     if isinstance(json_dict, dict):
                         attrs = {
                             k: json_dict[k] for k in self._json_attrs if k in json_dict
                         }
                         self._attributes = attrs
                     else:
-                        _LOGGER.warning("JSON result was not a dictionary")
+                        _LOGGER.warning(
+                            "JSON result was not a dictionary"
+                            " or list with 0th element a dictionary"
+                        )
                 except ValueError:
                     _LOGGER.warning("REST result could not be parsed as JSON")
                     _LOGGER.debug("Erroneous JSON: %s", value)

tests/components/rest/test_sensor.py

@@ -284,6 +284,26 @@ class TestRestSensor(unittest.TestCase):
         self.sensor.update()
         assert "some_json_value" == self.sensor.device_state_attributes["key"]
 
+    def test_update_with_json_attrs_list_dict(self):
+        """Test attributes get extracted from a JSON list[0] result."""
+        self.rest.update = Mock(
+            "rest.RestData.update",
+            side_effect=self.update_side_effect('[{ "key": "another_value" }]'),
+        )
+        self.sensor = rest.RestSensor(
+            self.hass,
+            self.rest,
+            self.name,
+            self.unit_of_measurement,
+            self.device_class,
+            None,
+            ["key"],
+            self.force_update,
+            self.resource_template,
+        )
+        self.sensor.update()
+        assert "another_value" == self.sensor.device_state_attributes["key"]
+
     @patch("homeassistant.components.rest.sensor._LOGGER")
     def test_update_with_json_attrs_no_data(self, mock_logger):
         """Test attributes when no JSON result fetched."""