exp = input("PLease input expression with space between operands and operator : ") exp = exp.split() def check_op(x): return True if x in ['+','-','*','/'] else print("wrong operator") or False def check_value(x): try: return float(x) except ValueError: return print("wrong input") or False result = 0 flag = False while len(exp) >= 3 and len(exp) %2: x = exp[0] op = exp[1] y = exp[2] x = check_value(x) y = check_value(y) if check_op(op) and x is not False and y is not False: if op == '+': result = x+y elif op == '-': result = x-y elif op == '*': result = x*y elif op == '/': if y == 0: print("cannot divide by zero") break else: result =x/y del exp[:2] exp[0] = result flag = True else : if flag: print(f"result : {exp[0]}") else : print("wrong expression input")