Postfix

# (A + B) * (C + D)
# https://gist.github.com/mycodeschool/7867739
class Stack:
    def __init__(self):
        self.top = -1
        self.stack = []

    def push(self, val):
        self.top += 1
        self.stack.append(val)

    def getTop(self):
        return self.stack[-1]

    def pop(self):
        self.top -= 1
        return self.stack.pop()

    def str(self):
        print("Current Stack: ", self.stack)
        print('Current Top: ', self.top)

    def empty(self):
        if self.top == -1 and len(self.stack) == 0:
            return True
        return False


def isOperator(x):
    if x == "+" or x == '-' or x == '*' or x == '/' or x == '^':
        return True
    return False

def isOperand(x):
    if x >= 'A' and x <= 'Z':
        return True
    elif x >= 'a' and x <= 'z':
        return True
    return False

def isOpeningParam(s):
    if s == '(':
        return True
    return False

def isClosingParam(s):
    if s == ')':
        return True
    return False

def getOpWeight(op):
    weight = -1
    if op == '+' or op == '-':
        weight = 1
    elif op == '*' or op == '/':
        weight = 2
    elif op == "^":
        weight = 3

    return weight


def hasHigherPrec(op1, op2):
    op1 = getOpWeight(op1)
    op2 = getOpWeight(op2)
    if op1 >= op2:
        return True
    return False

def convert_to_postfix(exp):
    stack = Stack()
    stack.push('(')
    exp += ')'
    result = ''
    for i in exp:
        if isOperand(i):
            result += i
        elif isOperator(i):
            while ((not stack.empty()) and isOperator(stack.getTop()) and hasHigherPrec(stack.getTop(), i)):
                result += stack.pop()
            stack.push(i)


        #param control
        elif isOpeningParam(i):
            stack.push(i)

        elif isClosingParam(i):
            while not isOpeningParam(stack.getTop()):
                result += stack.pop()
            #extram param pop()
            stack.pop()

    return result

if __name__ == '__main__':
    exp = "a+b*(c^d-e)^(f+g*h)-i"
    res = convert_to_postfix(exp)
    print(res)