For Java, you can try WhatsUp
For Python, see YowsUp.
Beware that WhatsApp threatens legal action against many of these library developers and does not officially support using the service this way.
I have also spoken directly with WhatsApp representatives who have said no commercial API use of WhatsApp is acceptable.
Also note that bulk messaging is against the WhatsApp terms of service.
There used to be a PHP implementation at WhatsAPI, and another Java implementation, WhatsApi4J. Both are no longer available due to legal threats.