This work is extracted from Praekelt PBC's work on MomConnect and WhatsApp. See the blog post for more details.
This does not work with a normal WhatsApp account, only the WhatsApp Business API.
Also has some support for sending message templates in bulk.
$ pip install wabclient[cli]
$ wabclient send --help
$ wabclient send \
--csv-file wa_ids.csv \
--token your-auth-token \
--namespace the-namespace \
--name the-element-name \
--rate-limit 60\60 \
--param "the first HSM template default param" \
--param "the second HSM template default param"