python if statement evaluation with multiple values

Question

I'm not exactly sure why but when I execute this section of code nothing happens.

while (True) :

    choice = str(input("Do you want to draw a spirograph? (Y/N) "))

    if choice == 'n' or 'N' :
        break

    elif choice == 'y' or 'Y' :    

       <CODE>

    else :
        print("Please enter a valid command.")
        choice = input("Do you want to draw a spirograph? (Y/N)")

Edit your code section and add while line to it. I don't do this myself cause your problem may rely on it. — Mehraban
– Mehraban, Commented Oct 7, 2014 at 4:52
So many SO questions would be avoided in Python self-linted this case.. — user2864740
– user2864740, Commented Oct 7, 2014 at 4:59
FWIW, you don't need parenthesis around your predicate. while True: is better. — rahmu
– rahmu, Commented Oct 7, 2014 at 5:00
possible duplicate of How do I test one variable against multiple values? — user2864740
– user2864740, Commented Oct 7, 2014 at 5:02
(And see the many linked answers on the duplicate such as stackoverflow.com/questions/20002503/…) — user2864740
– user2864740, Commented Oct 7, 2014 at 5:03

Anshul Goyal · Accepted Answer · 2014-10-07 09:12:10Z

12

It won't work because the 'N' literal always evaluates to True within your if statement.

Your if condition currently stands as if choice == 'n' or 'N' :, which is equivalent to if (choice == 'n') or ('N'), which will always evaluate to True irrespective of the value of variable choice, since the literal 'N' always evaluates to True.

Instead, use one of the following

if choice == 'n' or choice == 'N' :
if choice in 'nN' :
if choice in ('n', 'N') :

The same holds for your elif block as well. You can read more about Truth Value testing here.

edited Oct 7, 2014 at 9:12

answered Oct 7, 2014 at 4:53

Anshul Goyal

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Comments

Nick Russo · Accepted Answer · 2014-10-07 04:55:48Z

5

This expression doesn't do what you want:

choice == 'n' or 'N'

It is interpretted as this:

(choice == 'n') or 'N'

You might want to try this instead:

choice in 'nN'

answered Oct 7, 2014 at 4:55

Nick Russo

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