1.  from expStackModule import expStack
2.  opStk = expStack()
3.  def infixConvert(infixExp):
4.      pr = {}
5.      pr["*"] = 5
6.      pr["/"] = 5
7.      pr["+"] = 4
8.      pr["-"] = 4
9.      pr["("] = 1 
10.     postExp = []
11.     digits = "012345678"
12.     alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
13.     letters =  "abcdefghijklmnopqrstuvwxyz"
14.     for symbol in infixExp:  
15.         if symbol in alphabet or symbol in digits or symbol in letters:
16.            postExp.append(symbol)
17.         elif symbol == '(':
18.            opStk.push(symbol)
19.         elif symbol == ')':
20.            element = opStk.pop()
21.            while element != '(':
22.                postExp.append(element)
23.                element = opStk.pop()
24.         else:
25.            while not opStk.isEmpty() and (pr[opStk.top()] >= pr[symbol]):
26.                 postExp.append(opStk.pop())
27.            opStk.push(symbol)
28.     while not opStk.isEmpty():
29.       postExp.append(opStk.pop())
30.     return " ".join(postExp)
31.  infixExp = input("Enter an infix expression: ")
32.  print("Postfix expression is: ", infixConvert(infixExp))