convert infix to postfix

/* C++ implementation to convert  
 infix expression to postfix*/
// Note that here we use std::stack   
// for Stack operations 
#include<bits/stdc++.h> 
using namespace std; 
  
//Function to return precedence of operators 
int prec(char c) 
{ 
    if(c == '^') 
    return 3; 
    else if(c == '*' || c == '/') 
    return 2; 
    else if(c == '+' || c == '-') 
    return 1; 
    else
    return -1; 
} 
  
// The main function to convert infix expression 
//to postfix expression 
void infixToPostfix(string s) 
{ 
    std::stack<char> st; 
    st.push('N'); 
    int l = s.length(); 
    string ns; 
    for(int i = 0; i < l; i++) 
    { 
          
        // If the scanned character is  
        // an operand, add it to output string. 
        if((s[i] >= 'a' && s[i] <= 'z') ||  
           (s[i] >= 'A' && s[i] <= 'Z')) 
        ns+=s[i]; 
  
        // If the scanned character is an  
        // ‘(‘, push it to the stack. 
        else if(s[i] == '(') 
          
        st.push('('); 
          
        // If the scanned character is an ‘)’,  
        // pop and to output string from the stack 
        // until an ‘(‘ is encountered. 
        else if(s[i] == ')') 
        { 
            while(st.top() != 'N' && st.top() != '(') 
            { 
                char c = st.top(); 
                st.pop(); 
               ns += c; 
            } 
            if(st.top() == '(') 
            { 
                char c = st.top(); 
                st.pop(); 
            } 
        } 
          
        //If an operator is scanned 
        else{ 
            while(st.top() != 'N' && prec(s[i]) <=  
                                   prec(st.top())) 
            { 
                char c = st.top(); 
                st.pop(); 
                ns += c; 
            } 
            st.push(s[i]); 
        } 
  
    } 
    
    // Pop all the remaining elements from the stack 
    while(st.top() != 'N') 
    { 
        char c = st.top(); 
        st.pop(); 
        ns += c; 
    } 
      
    cout << ns << endl; 
  
} 
  
//Driver program to test above functions 
int main() 
{ 
    string exp = "a+b*(c^d-e)^(f+g*h)-i"; 
    infixToPostfix(exp); 
    return 0; 
} 
// This code is contributed by Gautam Singh 

"""
Author : ITVoyagers (itvoyagers.in)

Date :31st October 2019

Description : Program to show use of stack in infix to postfix conversion using python.
"""
class infix_to_postfix:
    precedence={'^':5,'*':4,'/':4,'+':3,'-':3,'(':2,')':1}
    def __init__(self):
        self.items=[]
        self.size=-1
    def push(self,value):
        self.items.append(value)
        self.size+=1
    def pop(self):
        if self.isempty():
            return 0
        else:
            self.size-=1
            return self.items.pop()
    def isempty(self):
        if(self.size==-1):
            return True
        else:
            return False
    def seek(self):
        if self.isempty():
            return false
        else:
            return self.items[self.size]
    def isOperand(self,i):
        if i in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ':
            return True
        else:
            return False
    def infixtopostfix (self,expr):
        postfix=""
        print('postfix expression after every iteration is:')
        for i in expr:
            if(len(expr)%2==0):
                print("Incorrect infix expr")
                return False
            elif(self.isOperand(i)):
                postfix +=i
            elif(i in '+-*/^'):
                while(len(self.items)and self.precedence[i]<=self.precedence[self.seek()]):
                    postfix+=self.pop()
                self.push(i)
            elif i is '(':
                self.push(i)
            elif i is ')':
                o=self.pop()
                while o!='(':
                    postfix +=o
                    o=self.pop()
            print(postfix)
                #end of for
        while len(self.items):
            if(self.seek()=='('):
                self.pop()
            else:
                postfix+=self.pop()
        return postfix
s=infix_to_postfix()
expr=input('enter the expression ')
result=s.infixtopostfix(expr)
if (result!=False):
    print("the postfix expr of :",expr,"is",result)