While loop to check for valid user input? [duplicate]

Answer 1

The very simple solution for this is to initialize some variable at the before the loop kicks in:

choice=''

#This means that choice is False now

while not choice:
    choice=input("Enjoying the course? (y/n)")
        if choice in ("yn")
            #any set of instructions
        else:
            print("Sorry, I didn't catch that. Enter again: ")
            choice=""

What this while conditional statement means is that as long as choice variable is false--doesn't have any value means choice=''-- ,then proceeds #with the loop If the choice have any value then proceed with enters the loop body and check the value for specific input, if the input doesn't fulfill the required value then reset the choice variable to False value again to continue prompts user until a correct input is supplied

Answer 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: ")

Answer 3

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).