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While the loop is checking if the user input is correct?

Python newbie is so sorry I'm sure this is a stupid question, but I can't solve the following problem in a tutorial that asks me to use a while loop to validate user input.

(using Python2.7)

Here's my code, but it doesn't work as expected:

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 version is output 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 is obviously wrong - the loop should end when the user types "y" or "n", but I'm not sure how. What am I doing wrong here?

Note: the task requires me to use both operator !=

andloop_condition

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3 answers


Shorter solution

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

What is your code doing wrong

As far as your code is concerned, you can add printing like this:

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 is:



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, in your code where the question comes up, there is a first step and your answer is initializing the value choice

. This is what you are doing wrong.

Solution with !=

andloop_condition

If you need to use both the operator !=

and loop_condition

, then you must enter the 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).

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You can use 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: ")
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The simplest solution for this is to initialize some variable in a step before the loop starts:

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=""

The fact that this conditional operator means that as long as the choice variable is false - it does not matter means the choice = '' - then continues # with a loop If the choice has any value, then proceed to enter the body of the loop and check the value for a particular input if the input does not match the required value then reset the selection variable to False again to continue prompting the user until the correct input is set

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