expressionevaluation

def infixtopostfix(infix):
    oper_dic = {'/':1,'*':1,'+':2,'-':2}
    stack=[]
    postexp = ''
    postfix = []
    for i in range(len(infix)):
        if infix[i] not in oper_dic:
            n=i
            #postfix.append(infix[i])
            while(not infix[i] not in oper_dic):
                i+=1
            postfix.append(infix[n:i+1])
        else:
            if(len(stack)==0):
                stack.append(infix[i])
            else:
                if oper_dic[stack[-1]] < oper_dic[infix[i]] :
                    for _ in range(len(stack)):
                        postfix.append(stack.pop())
                    
                
                    stack.append(infix[i])
                else:
                    stack.append(infix[i])
                
    for _ in range(len(stack)):
        postfix.append(stack.pop())        
        
    for i in postfix:
        postexp+=i
    return postexp
    
    
def exp_evaluation(exp):
    check=['*','/','+','-']
    result1 = infixtopostfix(exp)
   
    stack1 = []
    for i in range(len(result1)):
        if result1[i] not in check:
            stack.append(result1[i])
        else:
            opd2 = stack.pop()
            opd1 = stack.pop()
            stack.append(str(eval(opd1+result1[i]+opd2)))
            
            
    result = int(stack[-1])
    return result
   
   
re = exp_evaluation('1+2*3-4*5')

re
-13