Python Retrieve values from List in a Specific order

I have a Python program to get data from a JSON file and then store it into a list in post fix order. However now, I am trying to put the data into a new list which is in readable math notation. The issue is that I know that I need to find the first operator and then find the previous two numbers - I can do that for the first set however the recursion past that point is not working and I can't figure out why!I have a Python program to get data from a JSON