Welcome to the sixth lesson in our course, 'Introduction to DynamoDB with AWS SDK for Python'. Up to this point, we've explored how to set up your environment with DynamoDB and Boto3, how to create and configure tables, and how to insert and retrieve data from these tables. Today, we're delving deeper into updating and deleting items from DynamoDB tables using AWS's Boto3 library in Python. We'll also review how to delete multiple items at once. The ability to modify data is crucial when managing databases, especially when handling large quantities of data in the cloud.

In Boto3, the update_item method allows for modifications to items in a DynamoDB table. This method requires the primary key of the item to be updated and an UpdateExpression that defines the changes to be applied—whether setting new values, removing attributes, or modifying lists or set attributes.

Here's an example of updating a post in the 'UserPosts' table where 'John' is the primary key's username and '1' is the post_id:

This operation updates the 'content' of John's post. Note that the full primary key must be specified for updates. Additionally, update_item operations consume write capacity units, and careful consideration is required to manage these costs. Aliases and reserved words must be handled carefully in expressions, and it's also possible to specify the consistency of the read after an update if required.