试试看：

if answer in ["yes","Yes","YES"]:
            OR
if answer == "yes" or answer=="Yes" or answer=="YES":

而不是。

if answer == "yes" or "Yes" or "YES":

而不是使用if answer == "yes" or "Yes" or "YES":.你应该试试
if answer == "yes" or answer == "Yes" or answer == "YES":.
或者使用python内置的方法lower()，这样就可以将输入小写

x = int(input("Insert price for your product :"))

print ("Does your product include taxes?")
answer = input(" yes or no ").lower()
if answer == "yes":
    print ("finel price is : ", x, "\nthe tax is :" ,x*0.17)
elif answer == "no":
     print ("finel price is : ", x*1.17, "\nthe taxes is ", x*0.17)
else:
    print ("Your answer is not according to the dictionary - try agin")

这是语法上的问题。

if answer == "yes" or "Yes" or "YES":

在Python中，在这个上下文中，每次使用什么变量时，都需要详细说明，例如：

if answer == "yes" or answer== "Yes" or answer== "YES":

也可以采用其他格式，例如：

answer = answer.lower()
if answer == "yes":
    print ("final price is : ", x, "\nthe tax is : " , x*0.17)
elif answer == "no":
    print ("final price is : ", x*1.17, "\nthe tax is : ", x*0.17)
else:
    print ("Your answer is not according to the dictionary - try again")

这个解决方案将把answer全部改为小写，这允许人们也写一些东西，比如YeS或yeS。2这也使代码看起来不那么混乱。