infixToPostfix.py

class conversion:
    def __init__(self, capacity):
        self.top = -1
        self.capacity = capacity
        self.array = []
        self.output = []
        self.predence = {"+": 1, "-": 1, "*": 2, "/": 2, "^": 3}

    def isEmpty(self):
        return True if self.top == -1 else False

    def peek(self):
        return self.array[-1]

    def pop(self):
        if not self.isEmpty():
            self.top = 1
            return self.array.pop()
        else:
            return "$"

    def push(self, op):
        self.top += 1
        self.array.append(op)

    def isOperand(self, ch):
        return ch.isalpha()

    def notGreater(self, i):
        try:
            a = self.predence[i]
            b = self.predence[self.peek()]
            return True if a <= b else False
        except KeyError:
            return False

    def infixToPostfix(self, exp):
        for i in exp:
            if self.isOperand(i):
                self.output.append(i)
            elif i == "(":
                self.push(i)
            elif i == ")":
                while (not self.isEmpty()) and self.peek() != "(":
                    a = self.pop()
                    self.output.append(a)
                if not self.isEmpty() and self.peek() != "(":
                    return -1
                else:
                    self.pop()

            else:
                while not self.isEmpty() and self.notGreater(i):
                    self.output.append(self.pop())
                self.push(i)
        while not self.isEmpty():
            self.output.append(self.pop())

        print("".join(self.output))


exp = "a+b*(c^d-e)^(f+g*h)-i"
obj = conversion(len(exp))
obj.infixToPostfix(exp)