The thing is I don’t want to accidentially match new messages in the future that might sound similar, something like “Xyz just subscribed to [Hosting channel]”. Your example is especially error prone to newly added twitchnotify messages.
I’d rather retroactively manually increase a subscription in the database than take it away.
This is the current code, using regex is perfectly fine and more idiomatic:
match = re.match(r"^(.*?) just subscribed( with Twitch Prime)?!\s*$", message)
if match:
return {"name": match.group(1), "months_in_a_row": 1}