Here is one I made a while ago which will stream new blockchain posts and checks if the posts contains the "introduceyourself" tag. If the post contains the tag the bot comments a welcoming message on the post. But this is a old piece of code I wrote so there's a chance that it might be outdated by now . Hope this can serve as a guideline for what you'd like to do.

https://github.com/steandwt/Steemit-Welcome-Bot/blob/master/welcomeBot.py