infix to postfix python code

class stack:
def __init__(self):
    self.item = []

def push(self,it):
    self.item.append(it)
def peek(self):
    if self.isempty() == True:
        return 0
    return self.item[-1]

def pop(self):
    if self.isempty() == True:
        return 0
    return(self.item.pop())

def length(self):
    return (len(self.item))


def isempty(self):
    if self.item == []:
        return True
    else:
        return False

def display(self):
    if self.isempty()== True:
        return
    temps = stack()
    while(self.isempty() != True):
        x = self.peek()
        print("~",x)
        temps.push(x)
        self.pop()
    while(temps.isempty() != True):
        x = temps.peek()
        self.push(x)
        temps.pop()


def isOperand(self, ch): 
    return ch.isalpha()
def notGreater(self, i):
    precedence = {'+':1, '-':1, '*':2, '/':2, '%':2, '^':3}
    if self.peek() == '(':
        return False
    a = precedence[i]
    b = precedence[self.peek()] 
    if a  <= b:
        return True
    else:
        return False
        


def infixToPostfix(self, exp):
    output = ""
    
    for i in exp:
        
        if self.isOperand(i) == True: # check if operand add to output
            print(i,"~ Operand push to stack")
            output = output + i

        # If the character is an '(', push it to stack 
        elif i  == '(':
            self.push(i)
            print(i," ~ Found ( push into stack")

        elif i == ')':  # if ')' pop till '('
            while( self.isempty() != True and self.peek() != '('):
                n = self.pop() 
                output = output + n
                print(n, "~ Operator popped from stack")
            if (self.isempty() != True and self.peek() != '('):
                print("_________")
                return -1
            else:
                x = self.pop()
                print(x, "Popping and deleting (")
        else: 
            while(self.isempty() != True and self.notGreater(i)):
                c = self.pop()
                output = output + c
                print(c,"Operator popped after checking precedence from stack")
            self.push(i)
            print(i,"Operator pushed to stack")

    # pop all the operator from the stack 
    while self.isempty() != True:
        xx = self.pop()
        output = output + xx
        print(xx,"~ pop at last")
    print(output)
    self.display()
st = stack()
st.infixToPostfix("a+(b*c)")