How to update metadata of an existing object in AWS S3 using python boto3?

boto3 documentation does not clearly specify how to update the user metadata of an already existing S3 Object.

Answer

It can be done using the copy_from() method –

import boto3

s3 = boto3.resource('s3')
s3_object = s3.Object('bucket-name', 'key')
s3_object.metadata.update({'id':'value'})
s3_object.copy_from(CopySource={'Bucket':'bucket-name', 'Key':'key'}, Metadata=s3_object.metadata, MetadataDirective='REPLACE')