如何通过 Python SDK 获取 Collection 中已存在的 Doc

collection.fetch(    ids: Union[str, List[str]],    partition: Optional[str] = None,    async_req: bool = False) -> DashVectorResponse

import dashvector
client = dashvector.Client(    api_key='YOUR_API_KEY',    endpoint='YOUR_CLUSTER_ENDPOINT')collection = client.get(name='quickstart')
doc_id = '1'docs = collection.fetch(doc_id)# 判断fetch接口是否成功if docs:    print('fetch success')    # 判断fetch的doc是否存在，如果指定的ID不存在，则返回的output为空    if doc_id in docs:        doc = docs[doc_id]        print(doc.id)        print(doc.vector)        print(doc.fields)    # 遍历返回结果    for id in docs:        print(docs[id])
# 批量fetchdocs = collection.fetch(['1','2'])