Modify the Metadata of an Existing Object

Problem

You want to change the metadata associated with an existing object in S3.

Solution

Use the COPY directive to do an in-place copy of the object with the new metadata.

Discussion

The metadata for an object is defined when the object is created in S3. In the past, if you ever wanted to change the metadata, you had to upload the entire object again. However, the COPY operation now provides a way to change the metadata without incurring the time and cost of uploading the object data.

Example 3-7. Modify the Metadata of an Existing Object

import boto

def modify_metadata(bucket_name,
                    key_name,
                    metadata):
    """
    Update the metadata with an existing object.

    bucket_name   The name of the S3 Bucket.
    key_name      The name of the object containing the data in S3.
    metadata      A Python dict object containing the new metadata.
                  For example: {'key1':'value1', 'key2':'value2'}
    """
    s3 = boto.connect_s3()
    bucket = s3.lookup(bucket_name)

    # Lookup the existing object in S3
    key = bucket.lookup(key_name)

    # Copy the key back on to itself, with new metadata
    key.copy(bucket.name, key.name, metadata, preserve_acl=True)

    return key