3.9.2-infixToPsotfix.py

#! /usr/bin/env python3
# 3.9-Infix Expressions To Postfix Expressions
from Stack import Stack

def infixToPostfix(infixExpr):
    prec = {}
    prec['*'] = 3
    prec['/'] = 3
    prec['+'] = 2
    prec['-'] = 2
    prec['('] = 1
    opStack = Stack()
    postfixList = []
    tokenList = infixExpr.split()

    for token in tokenList:
        if token in "ABCDEFGHIJKLMNOPQRSTUVWXYX" or token in "0123456789":
            postfixList.append(token)
        elif token == "(":
            opStack.push(token)
        elif token == ")":
            topToken = opStack.pop()
            while topToken != '(':
                postfixList.append(topToken)
                topToken = opStack.pop()
        else:
            while (not opStack.isEmpty()) and prec[opStack.peek()] >= prec[token]:
                postfixList.append(opStack.pop())
            opStack.push(token)

    while not opStack.isEmpty():
        postfixList.append(opStack.pop())

    return " ".join(postfixList)
s = input("Pleast input a infix Expression:")
print("The Postfix Expression Is :", infixToPostfix(s))