code: def once(self, event: str, *handlers: T.Callable) -> T.Callable:
          
  
          def _once_wrapper(*handlers: T.Callable) -> T.Callable:
              """Wrapper for 'once' decorator"""
  
              def _wrapper(*args: T.Any, **kw: T.Any) -> None:
                  """Wrapper that unregisters itself before executing
                  the handlers"""
  
                  self.off(event, _wrapper)
                  for handler in handlers:
                      handler(*args, **kw)
  
              return _wrapper
  
          if handlers:
              return self.on(event, _once_wrapper(*handlers))
          return lambda x: self.on(event, _once_wrapper(x))
docs: Registers one or more handlers to a specified event, but
          removes them when the event is first triggered.
          This method may as well be used as a decorator for the handler.