A simple script that checks the host's current public IP via https://ipify.org and uses subreg.cz's SOAP API to create/update a DNS record pointing to said IP. Depends on zeep.
Before running the script you need to rename settings.dist.ini to settings.ini and edit it appropriately. For 'sub.example.org' the domain field should be 'example.org' and subdomain is 'sub'.