Is = '1 + 1 + 1 + 1' Is=Is.split() result = None while (len(Is)<=3): x= Is[0] op= Is[1] y= Is[2] if type(float(x)) == float and type(float(y)) == float: x=float(x) y=float(y) if op in ['+','-','*','/']: if op =='+': result=x+y if op =='-': result=x-y if op =='*': result=x*y if op == '/': result=x/y else: print("wrong operator") else: print("wrong operand") del Is[:2] Is[0]=result print (result) result = None Is ='1 + 1 + 1' Is =Is.split() while (len(Is) >=3): x=Is[0] op=Is[1] y=Is[2] if type(float(x)) == float and type(float(y)) == float: x=float(x) y=float(y) if op in ['+','-','*','/']: if op =='+': result=x+y if op =='-': result=x-y if op =='*': result=x*y if op == '/': result=x/y else: print("wrong operator!") break else: print("wrong data type") break del Is[:2] Is[0]=result if len(Is) ==2: print('wrong operand') break if len(Is) == 1: break else: print("wrong operand") print (result) result = None Is ='1 + 1 + 1 + 1' Is =Is.split() def check_float(data): try: float(data) return True except ValueError: print("invalid input") return False while (len(Is) >=3): x=Is[0] op=Is[1] y=Is[2] if check_float(x) and check_float(y): x=float(x) y=float(y) if op in ['+','-','*','/']: if op =='+': result=x+y if op =='-': result=x-y if op =='*': result=x*y if op == '/': result=x/y else: print("wrong operator!") break else: print("wrong data type") break del Is[:2] Is[0]=result if len(Is) ==2: print('wrong operand') break if len(Is) == 1: break else: print("wrong operand") print (result)