While loop to check for valid user input?

Question

Python newbie here so sorry for what I'm sure is a stupid question, but I can't seem to solve the following challenge in a tutorial that is asking me to use a while loop to check for valid user input.

(using Python2.7)

Here's my code, but it's not working properly:

choice = raw_input('Enjoying the course? (y/n)')
student_surveyPromptOn = True
while student_surveyPromptOn:
    if choice != raw_input('Enjoying the course? (y/n)'):
        print("Sorry, I didn't catch that. Enter again: ")
    else:
        student_surveyPromptOn = False 

The above prints out to the console:

Enjoying the course? (y/n) y
Enjoying the course? (y/n) n
Sorry, I didn't catch that. Enter again: 
Enjoying the course? (y/n) x
Sorry, I didn't catch that. Enter again: 
Enjoying the course? (y/n)  

Which obviously isn't correct — the loop should end when the user enters either 'y' or 'n' but I'm not sure how to do this. What am I doing wrong here?

Note: the challenge requires me to use both the != operator and the loop_condition

Solution 1

A shorter solution

while raw_input("Enjoying the course? (y/n) ") not in ('y', 'n'):
    print("Sorry, I didn't catch that. Enter again:")

What your code is doing wrong

With regard to your code, you can add some print as follow:

choice = raw_input("Enjoying the course? (y/n) ")
print("choice = " + choice)
student_surveyPromptOn = True
while student_surveyPromptOn:
    input = raw_input("Enjoying the course? (y/n) ")
    print("input = " + input)
    if choice != input:
        print("Sorry, I didn't catch that. Enter again:")
    else:
        student_surveyPromptOn = False

The above prints out:

Enjoying the course? (y/n) y
choice = y
Enjoying the course? (y/n) n
choice = y
input = n
Sorry, I didn't catch that. Enter again:
Enjoying the course? (y/n) x
choice = y
input = x
Sorry, I didn't catch that. Enter again:
Enjoying the course? (y/n) 

As you can see, there is a first step in your code where the question appears and your answer initializes the value of choice. This is what you are doing wrong.

A solution with != and loop_condition

If you have to use both the != operator and the loop_condition then you should code:

student_surveyPromptOn = True
while student_surveyPromptOn:
    choice = raw_input("Enjoying the course? (y/n) ")
    if choice != 'y' and choice != 'n':
        print("Sorry, I didn't catch that. Enter again:")
    else:
        student_surveyPromptOn = False

However, it seems to me that both Cyber's solution and my shorter solution are more elegant (i.e. more pythonic).

Solution 2

You can use the condition

while choice not in ('y', 'n'):
    choice = raw_input('Enjoying the course? (y/n)')
    if not choice:
        print("Sorry, I didn't catch that. Enter again: ")

Comments

[AdjunctProfessorFalcon]

Thank you for the help! I tried the solution with the != and loop_condition but when user enters either 'y' or 'n', it asks the question again. How can I get the loop to quit after someone enters either 'y' or 'n' the first time the question is asked?

[Flabetvibes]

You're welcome. Which code are you talking about? My solution with != and loop_condition does not ask the question again after someone enters either 'y' or 'n'. I suppose you have tried something different. If so, please could you edit your question to add this piece of code?