events from subscriptions. The registered callback function will be called
when an event is received.
+ It should be noted that subscribe_channel must be called before calling
+ start_event_listener to do at least one subscription before event loop
+ starts.
+
Raises:
SdlTypeError: If function's argument is of an inappropriate type.
NotConnected: If SDL is not connected to the backend data storage.
event loop. Calling this function after start_event_listener raises an exception.
If there are no notifications, these returns None.
+ It should be noted that subscribe_channel must be called before calling of the
+ handle_events in an event loop. At least one subscription must be done before
+ events handling starts.
+
Returns:
Tuple: (channel: str, message: str)