def unregister(self, event):
        """
        Remove all registered handlers for an event.
        Silent return when event was not registered.

        Usage:

            dispatch.unregister("my_event")
            dispatch.unregister("my_event")  # no-op

        """
        if self.running:
            raise RuntimeError("Can't unregister while running")
        self._handlers.pop(event, None)