How to implement access control list using mininet and PoX controller

Question

I read what is in mininet documentation but didn't understand alot, I'm using a simple typology just 2 switches and each switch is connected to 2 hosts all I want to do is just deny traffic from any host to host4 or something like that, I hope I get an answer soon cuz I have a project on this

I tried to create something with python but I couldn't run it