Python 检索保存到blobstore的照片的元数据

我正在使用将照片上载到blobstore。数据库中有一些元数据

content_type: The content type of the blob.
creation: The creation date of the blob, or when it was uploaded.
filename: The file name that the user selected from their machine.
size: The size of the uncompressed blob.
md5_hash: The MD5 hash value of the uploaded blob.

我的问题是如何从plupload或服务器端获取照片的其他元数据？具体地说，我需要检索“description”元数据字段。

我将使用以下内容：

blob_reader = blobstore.BlobReader(blob_key)
blob_reader_data = StringIO.StringIO(blob_reader.read())
tags = exifread.process_file(blob_reader_data)

它返回的标记对象包含您正在查找的元数据