Agents will notify the pub they want to leave

def exit(self, pub_id, *node_ids):
        '''Agents will notify the pub they want to leave'''
        try:
            pub = self['pubs'][pub_id]
        except KeyError:
            raise ValueError('Pub {} is not available'.format(pub_id))
        for node_id in node_ids:
            node = self.get_agent(node_id)
            if pub_id == node['pub']:
                del node['pub']
                pub['occupancy'] -= 1