infix_to_postfix.py

"""
Output:

Enter an Infix Equation = a + b ^c
 Symbol  |  Stack  | Postfix
----------------------------
   a     |         | a
   +     | +       | a
   b     | +       | ab
   ^     | +^      | ab
   c     | +^      | abc
         | +       | abc^
         |         | abc^+

	 a+b^c -> abc^+
"""

def infix_2_postfix(Infix):
    Stack = []
    Postfix = []
    priority = {'^':3, '*':2, '/':2, '%':2, '+':1, '-':1}       # Priority of each operator
    print_width = len(Infix) if(len(Infix)>7) else 7

    # Print table header for output
    print('Symbol'.center(8), 'Stack'.center(print_width), 'Postfix'.center(print_width), sep = " | ")
    print('-'*(print_width*3+7))

    for x in Infix:
        if(x.isalpha() or x.isdigit()): Postfix.append(x)       # if x is Alphabet / Digit, add it to Postfix
        elif(x == '('): Stack.append(x)                         # if x is "(" push to Stack
        elif(x == ')'):                                         # if x is ")" pop stack until "(" is encountered
            while(Stack[-1] != '('):
                Postfix.append( Stack.pop() )                   #Pop stack & add the content to Postfix
            Stack.pop()
        else:
            if(len(Stack)==0): Stack.append(x)                  #If stack is empty, push x to stack
            else:
                while( len(Stack) > 0 and priority[x] <= priority[Stack[-1]]):      # while priority of x is not greater than priority of element in the stack
                    Postfix.append( Stack.pop() )                                   # pop stack & add to Postfix
                Stack.append(x)                                 # push x to stack

        print(x.center(8), (''.join(Stack)).ljust(print_width), (''.join(Postfix)).ljust(print_width), sep = " | ")         # Output in tabular format

    while(len(Stack) > 0):                                  # while stack is not empty
        Postfix.append( Stack.pop() )                       # pop stack & add to Postfix
        print(' '.center(8), (''.join(Stack)).ljust(print_width), (''.join(Postfix)).ljust(print_width), sep = " | ")         # Output in tabular format

    return "".join(Postfix)             # return Postfix as str

Infix = input("\nEnter an Infix Equation = ")       #Input an Infix equation
Infix = "".join(Infix.split())                      #Remove spaces from the input
print("\n\t", Infix, "->", infix_2_postfix(Infix))