In almost every build your own SAAS tutorial or video I see python being used for the back end (I haven't used it before) i just want to understand what advantage does python provide
Advantages:
All that said I personally prefer Ruby on Rails for the backend (or both ends).
I think a big part of backend web dev with python is centered around the frameworks django and flask. I don't know much about django, but I know that flask is used by many top companies to build highly available rest apis. These apis are used to build their apps using a microservices architecture.
It's going to be the most popular programming language. Watch here:
https://www.reddit.com/r/Python/comments/d35ah4/this_video_shows_the_most_popular_programming/