陷入困境

Question

我无法通过while声明：

letter_grade=input("What is your letter grade(please use capitlization): ")
while letter_grade!="A" or "B+" or "B" or "C+" or "C" or "D" or "F":
    print ("Enter a valid letter")
    letter_grade=input("What is your letter grade(please use capitlization): ")

Answer 1

试试这个：

letter_grade=input("What is your letter grade(please use capitlization): ")
while letter_grade not in ["A","B+","B","C+","C","D","F"]:
    print ("Enter a valid letter")
    letter_grade=input("What is your letter grade(please use capitlization): ")

您当前的代码无法正常工作，因为您无法像您一样简化布尔语句。为了使你的工作成功，你必须将其改为：

letter_grade!="A" and letter_grade!="B+" and #etc.

您必须针对变量测试每个字母。

Answer 2

您似乎不理解逻辑语句的工作原理。您的行定义为：

while letter_grade!="A" or "B+" or "B" or "C+" or "C" or "D" or "F":

这总是返回true，因为它并不意味着你想要它。你想使用类似的东西：

while letter_grade!="A" and letter_grade!="B+" and letter_grade!="B": #etc

但为了便于阅读，我建议使用代码：

letter_grade=input("What is your letter grade(please use capitlization): ")
possible_grades = {"A","B+","B","C+","C","D","F"}
while letter_grade not in possible_grades:
    print ("Enter a valid letter")
    letter_grade=input("What is your letter grade(please use capitlization): ")

请注意，使用集合可以加快查找速度。