How to continue asking user for input until it is considered valid?

Question

My code is meant to ask a user to pick which household animal that is preferred. The answer should be either "cats" or "dogs".

household_animal = (input("Which household animal do you prefer?"))
if household_animal in ("cat", "dog"):
    print("Thanks for your input on which household animal you prefer!")
else:
    print("This is not a household animal, please pick again.")

I am uncertain about how to make the program continue to ask for input until the user picks either "cat" or "dog". If correct input is detected, it should no longer ask for more input.

How do I solve this?

Hint: You'll need to loop back around and ask the question again if it's not one of the answers you want. — Keith, Oct 03 '15 at 22:32
Possible duplicate of [Asking the user for input until they give a valid response](https://stackoverflow.com/questions/23294658/asking-the-user-for-input-until-they-give-a-valid-response) — ruohola, May 04 '19 at 14:20

score 1 · Answer 1 · answered Oct 03 '15 at 22:28

You need to ask iteratively using a loop:

household_animal = input("Which household animal do you prefer?")
while household_animal not in ("cat", "dog"):
    print("This is not a household animal, please pick again.")
    # pick again
    household_animal = input("Which household animal do you prefer?")
print("Thanks for your input on which household animal you prefer!")

score 1 · Answer 2 · answered Oct 03 '15 at 22:40

Explanation

Since you will need to keep asking for input until a suitable animal has been chosen, you should introduce some form of loop until that condition is met.

There are many ways to write such functionality, but what you are looking for is something such as the below.

household_animal = None

while household_animal not in ("cat", "dog"):
    if household_animal is not None:
      print ("This is not a household animal, please pick again.")

    household_animal = input ("Which household animal do you prefer?")

print ("Thanks for your input on which household animal you prefer!")

Note: The code will loop until household_animal is either "cat" or "dog", and display an error message if the user has written something which is not one of the two.

How to continue asking user for input until it is considered valid?

2 Answers2