def persist_instances(metamodel, path, mode='w'):
    '''
    Persist all instances in a *metamodel* by serializing them and saving to a 
    *path* on disk.
    '''
    with open(path, mode) as f:
        for inst in metamodel.instances:
            s = serialize_instance(inst)
            f.write(s)
Persist all instances in a *metamodel* by serializing them and saving to a 
    *path* on disk.