fix: handle UnitOfConductivity import

Move unit imports inside function and add fallback for older versions.

Resolves #123

custom_components/xiaomi_home/miot/miot_device.py

@@ -59,20 +59,6 @@ from homeassistant.const import (
     LIGHT_LUX,
     PERCENTAGE,
     SIGNAL_STRENGTH_DECIBELS,
-    UnitOfEnergy,
-    UnitOfElectricCurrent,
-    UnitOfElectricPotential,
-    UnitOfInformation,
-    UnitOfLength,
-    UnitOfMass,
-    UnitOfSpeed,
-    UnitOfTime,
-    UnitOfTemperature,
-    UnitOfPressure,
-    UnitOfPower,
-    UnitOfVolume,
-    UnitOfVolumeFlowRate,
-    UnitOfConductivity
 )
 from homeassistant.helpers.entity import DeviceInfo
 from homeassistant.components.switch import SwitchDeviceClass
@@ -505,7 +491,8 @@ class MIoTDevice:
             prop_access.add('read')
         if prop.writable:
             prop_access.add('write')
-        if prop_access != (SPEC_PROP_TRANS_MAP['entities'][platform]['access']):
+        if prop_access != (SPEC_PROP_TRANS_MAP[
+                'entities'][platform]['access']):
             return None
         if prop.format_ not in SPEC_PROP_TRANS_MAP[
                 'entities'][platform]['format']:
@@ -584,7 +571,24 @@ class MIoTDevice:
                 self.append_action(action=action)
 
     def unit_convert(self, spec_unit: str) -> Optional[str]:
-        return {
+        """Convert MIoT unit to Home Assistant unit."""
+        from homeassistant.const import (
+            UnitOfEnergy,
+            UnitOfElectricCurrent,
+            UnitOfElectricPotential,
+            UnitOfInformation,
+            UnitOfLength,
+            UnitOfMass,
+            UnitOfSpeed,
+            UnitOfTime,
+            UnitOfTemperature,
+            UnitOfPressure,
+            UnitOfPower,
+            UnitOfVolume,
+            UnitOfVolumeFlowRate,
+        )
+
+        unit_map = {
             'percentage': PERCENTAGE,
             'weeks': UnitOfTime.WEEKS,
             'days': UnitOfTime.DAYS,
@@ -616,11 +620,18 @@ class MIoTDevice:
             'm': UnitOfLength.METERS,
             'km': UnitOfLength.KILOMETERS,
             'm3/h': UnitOfVolumeFlowRate.CUBIC_METERS_PER_HOUR,
-            'μS/cm': UnitOfConductivity.MICROSIEMENS_PER_CM,
             'gram': UnitOfMass.GRAMS,
             'dB': SIGNAL_STRENGTH_DECIBELS,
             'kB': UnitOfInformation.KILOBYTES,
-        }.get(spec_unit, None)
+        }
+
+        try:
+            from homeassistant.const import UnitOfConductivity
+            unit_map['μS/cm'] = UnitOfConductivity.MICROSIEMENS_PER_CM
+        except ImportError:
+            unit_map['μS/cm'] = 'μS/cm'
+
+        return unit_map.get(spec_unit, None)
 
     def icon_convert(self, spec_unit: str) -> Optional[str]:
         if spec_unit in ['percentage']:
@@ -1170,8 +1181,8 @@ class MIoTEventEntity(Entity):
             handler=self.__on_device_state_changed)
         # Sub value changed
         self.miot_device.sub_event(
-            handler=self.__on_event_occurred, siid=self.service.iid,
-            eiid=self.spec.iid)
+            handler=self.__on_event_occurred,
+            siid=self.service.iid, eiid=self.spec.iid)
 
     async def async_will_remove_from_hass(self) -> None:
         self.miot_device.unsub_device_state(