Improve type hint in darksky sensor entity (#77035)

homeassistant/components/darksky/sensor.py

@@ -663,8 +663,7 @@ class DarkSkySensor(SensorEntity):
         self.forecast_data = forecast_data
         self.forecast_day = forecast_day
         self.forecast_hour = forecast_hour
-        self._icon = None
-        self._unit_of_measurement = None
+        self._icon: str | None = None
 
         if forecast_day is not None:
             self._attr_name = f"{name} {description.name} {forecast_day}d"
@@ -673,18 +672,13 @@ class DarkSkySensor(SensorEntity):
         else:
             self._attr_name = f"{name} {description.name}"
 
-    @property
-    def native_unit_of_measurement(self):
-        """Return the unit of measurement of this entity, if any."""
-        return self._unit_of_measurement
-
     @property
     def unit_system(self):
         """Return the unit system of this entity."""
         return self.forecast_data.unit_system
 
     @property
-    def entity_picture(self):
+    def entity_picture(self) -> str | None:
         """Return the entity picture to use in the frontend, if any."""
         if self._icon is None or "summary" not in self.entity_description.key:
             return None
@@ -694,13 +688,15 @@ class DarkSkySensor(SensorEntity):
 
         return None
 
-    def update_unit_of_measurement(self):
+    def update_unit_of_measurement(self) -> None:
         """Update units based on unit system."""
         unit_key = MAP_UNIT_SYSTEM.get(self.unit_system, "si_unit")
-        self._unit_of_measurement = getattr(self.entity_description, unit_key)
+        self._attr_native_unit_of_measurement = getattr(
+            self.entity_description, unit_key
+        )
 
     @property
-    def icon(self):
+    def icon(self) -> str | None:
         """Icon to use in the frontend, if any."""
         if (
             "summary" in self.entity_description.key
@@ -710,7 +706,7 @@ class DarkSkySensor(SensorEntity):
 
         return self.entity_description.icon
 
-    def update(self):
+    def update(self) -> None:
         """Get the latest data from Dark Sky and updates the states."""
         # Call the API for new forecast data. Each sensor will re-trigger this
         # same exact call, but that's fine. We cache results for a short period