Getting Stuck in a while loop

Question

I can't get past the while statement:

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): ")

`letter_grade!="A" or "B+" or "B" or "C+" or "C" or "D" or "F"` is equivalent to `letter_grade!="A" or True or True or True or True or True or True` — eyllanesc, Oct 30 '17 at 03:02
there is no error message whenever i enter any of these letter it repeats the loop even tho it should move on with the code — Donovan Johnson Jr., Oct 30 '17 at 03:02
Change `letter_grade!="A" or "B+" or "B" or "C+" or "C" or "D" or "F":` to `while letter_grade not in ["A", "B+", "B", "C+", "C", "D", "F"]:` — eyllanesc, Oct 30 '17 at 03:03
@aylianesc a set would be more appropriate in this case. See my answer. — scharette, Oct 30 '17 at 03:12

gommb · Accepted Answer · 2017-10-30T03:31:58.303

1

Try this:

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): ")

Your current code doesn't work since you can't simplify boolean statements like you have. To make what you have work you would have to change it to:

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

where you have to test every letter against the variable.

edited Oct 30 '17 at 03:31

answered Oct 30 '17 at 03:03

gommb

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Care to share what was wrong with his code? – everton Oct 30 '17 at 03:04
1

@everton `while letter_grade!="A" or "B+" or "B" or "C+" or "C" or "D" or "F"` here all the character/string represents True i.e. or "B+" or "B" or "C+" or "C" or "D" or "F" which was causing infinite while loop. – Mahesh Karia Oct 30 '17 at 03:06

score 1 · Answer 2 · edited Oct 30 '17 at 03:10

You seem to not understand how logical statements work. Your line is defined as:

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

This always returns true since it does not mean what you want it to be. You wanted to use something like that:

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

But for readability, I would recommend that code :

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): ")

Note that using a set will allow faster lookup.

Getting Stuck in a while loop

2 Answers2