@callback
def add_to_platform_start(self, hass: HomeAssistant, platform: EntityPlatform, parallel_updates: Optional[asyncio.Semaphore]) -> None:
    'Start adding an entity to a platform.'
    if self._added:
        raise HomeAssistantError(f'Entity {self.entity_id} cannot be added a second time to an entity platform')
    self.hass = hass
    self.platform = platform
    self.parallel_updates = parallel_updates
    self._added = True
Start adding an entity to a platform.
@callback
def add_to_platform_start(self, hass: HomeAssistant, platform: EntityPlatform, parallel_updates: Optional[asyncio.Semaphore]) -> None:
    
    if self._added:
        raise HomeAssistantError(f'Entity {self.entity_id} cannot be added a second time to an entity platform')
    self.hass = hass
    self.platform = platform
    self.parallel_updates = parallel_updates
    self._added = True