Transactions with DynamoDB library Boto3

The boto3 library does not provide any support for cross-table transactions like that supported by the Java client library you reference. DynamoDB itself does not natively support this functionality so transactions like this have to be implemented at the client layer and your tables much be designed to support the fields required by the client software.

It would certainly be possible to implement a Python transaction client similar to the Java one but as far as I know, no one has.

For people searching for transactions, this has now changed. AWS recently introduced DynamoDB Transactions. Boto will be updated to handle them.