Object Storage Service:Use OSS SDK for Python to manage object metadata

Objects stored in Object Storage Service (OSS) consist of keys, data, and object metadata. Object metadata describes object attributes. Object metadata includes standard HTTP headers and user metadata. You can create custom HTTP request policies such as object cache policies and forced object download policies by configuring standard HTTP headers. You can also configure user metadata for an object to identify the purposes or attributes of the object.

Usage notes

• In this topic, the public endpoint of the China (Hangzhou) region is used. If you want to access OSS from other Alibaba Cloud services in the same region as OSS, use an internal endpoint. For more information about OSS regions and endpoints, see Regions and endpoints.

• In this topic, an OSSClient instance is created by using an OSS endpoint. If you want to create an OSSClient instance by using custom domain names or Security Token Service (STS), see Initialization.

• To configure object metadata, you must have the oss:PutObject permission. To query object metadata, you must have the oss:GetObject permission. For more information, see Attach a custom policy to a RAM user.

Configure HTTP headers

The following sample code provides an example on how to configure HTTP headers for the exampleobject.txt object in the exampledir directory of the examplebucket bucket.

# -*- coding: utf-8 -*-
import oss2
from oss2.credentials import EnvironmentVariableCredentialsProvider

# Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured. 
auth = oss2.ProviderAuth(EnvironmentVariableCredentialsProvider())
# Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. 
# Specify the name of the bucket. 
bucket = oss2.Bucket(auth, 'https://oss-cn-hangzhou.aliyuncs.com', 'examplebucket')

# Specify the full path of the object. Example: exampledir/exampleobject.txt. Do not include the bucket name in the full path. 
object_name = 'exampledir/exampleobject.txt'
# Specify the string that you want to upload. 
content = '{"age": 1}'
# Configure HTTP headers. For example, set the Content-Type header to 'application/json; charset=utf-8'. 
bucket.put_object(object_name, content, headers={'Content-Type': 'application/json; charset=utf-8'})

Configure user metadata

The following sample code provides an example on how to configure user metadata for the exampleobject.txt object in the exampledir directory of the examplebucket bucket:

# -*- coding: utf-8 -*-
import oss2
from oss2.credentials import EnvironmentVariableCredentialsProvider

# Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured. 
auth = oss2.ProviderAuth(EnvironmentVariableCredentialsProvider())
# Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. 
# Specify the name of the bucket. 
bucket = oss2.Bucket(auth, 'https://oss-cn-hangzhou.aliyuncs.com', 'examplebucket')

# Specify the full path of the object. Example: exampledir/exampleobject.txt. Do not include the bucket name in the full path. 
object_name = 'exampledir/exampleobject.txt'
# Specify the string that you want to upload. 
content = 'a novel'
# Configure the user metadata. User metadata is configured by specifying custom headers prefixed with x-oss-meta-. Sample header: x-oss-meta-author. Sample value: O. Henry.  
bucket.put_object(object_name, content, headers={'x-oss-meta-author': 'O. Henry', 'Content-Type': 'application/json; charset=utf-8'})

Modify object metadata

The following sample code provides an example on how to modify the metadata of the exampleobject.txt object in the exampledir directory of the examplebucket bucket:

# -*- coding: utf-8 -*-
import oss2
from oss2.credentials import EnvironmentVariableCredentialsProvider

# Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured. 
auth = oss2.ProviderAuth(EnvironmentVariableCredentialsProvider())
# Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. 
# Specify the name of the bucket. 
bucket = oss2.Bucket(auth, 'https://oss-cn-hangzhou.aliyuncs.com', 'examplebucket')

# Specify the full path of the object. Example: exampledir/exampleobject.txt. Do not include the bucket name in the full path. 
object_name = 'exampledir/exampleobject.txt'
# Modify the object metadata. 
bucket.update_object_meta(object_name, {'x-oss-meta-author': 'O. Henry'})
# Each time you use the bucket.update_object_meta method, the user metadata is updated. 
bucket.update_object_meta(object_name, {'Content-Type': 'text/plain'})

Query object metadata

You can use the methods provided by OSS SDK for Python to query object metadata.

The following sample code provides an example on how to query the metadata of the exampleobject.txt object in the exampledir directory of the examplebucket bucket:

# -*- coding: utf-8 -*-
import oss2
from oss2.credentials import EnvironmentVariableCredentialsProvider

# Obtain access credentials from environment variables. Before you run the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured. 
auth = oss2.ProviderAuth(EnvironmentVariableCredentialsProvider())
# Specify the endpoint of the region in which the bucket is located. For example, if the bucket is located in the China (Hangzhou) region, set the endpoint to https://oss-cn-hangzhou.aliyuncs.com. 
# Specify the name of the bucket. 
bucket = oss2.Bucket(auth, 'https://oss-cn-hangzhou.aliyuncs.com', 'examplebucket')

# Specify the full path of the object. Example: exampledir/exampleobject.txt. Do not include the bucket name in the full path. 
object_name = 'exampledir/exampleobject.txt'

# Query part of the object metadata by using the get_object_meta method. 
simplifiedmeta = bucket.get_object_meta(object_name)
# Query the last modified time of the object. 
print(simplifiedmeta.headers['Last-Modified']) 
# Query the size of the object. 
print(simplifiedmeta.headers['Content-Length']) 
# Query the ETag of the object. 
print(simplifiedmeta.headers['ETag']) 
# Query the object metadata, including the last access time of the object, after you enable access tracking. You can use only OSS SDK for Python 2.16.1 or later to query the last access time of objects. 
print(simplifiedmeta.headers['x-oss-last-access-time'])

# Query all object metadata by using the head_object method. 
objectmeta = bucket.head_object(object_name)
# In this example, only part of the object metadata is displayed. You can add code lines to display other object metadata. 
print(objectmeta.headers['Content-Type']) 
print(objectmeta.headers['Last-Modified']) 
print(objectmeta.headers['x-oss-object-type'])

References

• For more information about object metadata, see Manage object metadata.

• For more information about the API operation that you can call to configure object metadata when you perform simple upload, see PutObject.

• For more information about the API operations that you can call to query object metadata, see GetObjectMeta and HeadObject.