Remove handler

        :param handler: callback
        :return:

def unregister(self, handler):
        """
        Remove handler

        :param handler: callback
        :return:
        """
        for handler_obj in self.handlers:
            registered = handler_obj.handler
            if handler is registered:
                self.handlers.remove(handler_obj)
                return True
        raise ValueError('This handler is not registered!')