Stacks in python (Postfix evaluation)

Hey everyone!

I need some help to complete this code i am doing for my programming class. I a working with stacks and need to create a program that evaluates postfix notations. I have input 'expressions.txt' file that has all the postfix notations i need to evaluate. My program evaluates 6 out of 10 notations, i need help to do the rest 4.

Attached along is the text file that contains postfix notations. I am attaching Stacks.py and ListNode.py files with changed file format to .txt so that i can upload them.

I am also pasting my driver.py program here. Any input is highly appreciated. Thanks in advance.

from Stack import *

def postFix(expression):
    myStack= Stack()
    tokenList= expression.split()

    for token in tokenList:
        if token.isdigit():
            myStack.push(int(token))
            
        elif token == '+':
            if not myStack.is_empty():
                x = myStack.pop()
            else:
                print("\nERROR: ", expression, "is an invalid postfix expression.")
                break
            if not myStack.is_empty():
                y = myStack.pop()
            else:
                print("\nERROR: ", expression, "is an invalid postfix expression.")
                break
            summ = x + y
            myStack.push(summ)
        elif token == '-':
            if not myStack.is_empty():
                x = myStack.pop()
            else:
                print("\nERROR: ", expression, "is an invalid postfix expression.")
                break
            if not myStack.is_empty():
                y = myStack.pop()
            else:
                print("\nERROR: ", expression, "is an invalid postfix expression.")
                break
            subs = y - x
            myStack.push(subs)
        elif token == '*':
            if not myStack.is_empty():
                x = myStack.pop()
            else:
                print("\nERROR: ", expression, "is an invalid postfix expression.")
                break
            if not myStack.is_empty():
                y = myStack.pop()
            else:
                print("\nERROR: ", expression, "is an invalid postfix expression.")
                break
            prod = x * y
            myStack.push(prod)
        elif token == '/':
            if not myStack.is_empty():
                x = myStack.pop()
            else:
                print("\nERROR: ", expression, "is an invalid postfix expression.")
                break
            if not myStack.is_empty():
                y = myStack.pop()
            else:
                print("\nERROR: ", expression, "is an invalid postfix expression.")
                break
            divi = y / x
            myStack.push(divi)
            
        else:
            print("\nERROR: ", expression, "is an invalid postfix expression.")
    return myStack.pop()
    

#Main program
FileName = input("Enter the name of the file containing postfix expressions: ")
user = open(FileName , 'r')
for each in user:
  line= each.strip()
  print ("\n","Expression: ",line, "\n", "Answer: ", postFix(line))
user.close()