Python检查Azure指定Blob是否存在并实现安全下载

在Azure存储容器的topview目录下存储了命名格式为<ID>_topview.png的图片文件，需要编写Python脚本依据给定的ID列表仅下载Azure中存在的对应图片。现有代码在目标Blob不存在时会抛出错误，尝试使用blob_client.exist()方法无效。

现有实现代码：

blob_service_client = BlobServiceClient.from_connection_string(imagedata_acc_string)
container_client = blob_service_client.get_container_client(imagedata_acc_container)

topviewfilepath =  "gt" + "/" + id + "_topview.png" #
blobfilepath = "topview/" + id + "_topview.png"    

blob_client = container_client.get_blob_client(blobfilepath)
with open(topviewfilepath, "wb") as data:
   myblob = blob_client.download_blob()
   myblob.readinto(data)

解决方案 #

方法一：使用正确的exists()方法检查Blob存在性 #

你之前使用的exist()是拼写错误，Azure Blob Storage Python SDK中BlobClient的正确方法是exists()（末尾带s），该方法会发送HEAD请求验证Blob是否存在，返回布尔值。

修改后的代码：

from azure.storage.blob import BlobServiceClient

# 初始化客户端
blob_service_client = BlobServiceClient.from_connection_string(imagedata_acc_string)
container_client = blob_service_client.get_container_client(imagedata_acc_container)

# 替换为实际的ID列表
id_list = ["id_001", "id_002", "id_003"]

for id in id_list:
    topviewfilepath = f"gt/{id}_topview.png"
    blobfilepath = f"topview/{id}_topview.png"
    
    blob_client = container_client.get_blob_client(blobfilepath)
    
    # 检查Blob是否存在
    if blob_client.exists():
        with open(topviewfilepath, "wb") as data:
            myblob = blob_client.download_blob()
            myblob.readinto(data)
        print(f"已下载：{blobfilepath}")
    else:
        print(f"Blob不存在，跳过：{blobfilepath}")

方法二：捕获异常实现无感知跳过 #

如果需要减少额外的请求次数，可以直接尝试下载操作，当Blob不存在时捕获ResourceNotFoundError异常，这种方式避免了单独的存在性检查请求，适合批量处理场景。

代码示例：

from azure.storage.blob import BlobServiceClient, ResourceNotFoundError

# 初始化客户端
blob_service_client = BlobServiceClient.from_connection_string(imagedata_acc_string)
container_client = blob_service_client.get_container_client(imagedata_acc_container)

# 替换为实际的ID列表
id_list = ["id_001", "id_002", "id_003"]

for id in id_list:
    topviewfilepath = f"gt/{id}_topview.png"
    blobfilepath = f"topview/{id}_topview.png"
    
    blob_client = container_client.get_blob_client(blobfilepath)
    
    try:
        with open(topviewfilepath, "wb") as data:
            myblob = blob_client.download_blob()
            myblob.readinto(data)
        print(f"已下载：{blobfilepath}")
    except ResourceNotFoundError:
        print(f"Blob不存在，跳过：{blobfilepath}")

内容的提问来源于stack exchange，提问作者Sulphur