why is or not working for me in python?

Question

this is my code:

for count in range(NOI):
        ig=input("enter a GTIN code: ")
        while ig!=("21356797"):
                print("incorrect")
                ig=input("enter a GTIN code: ")
                count =count+1

and this is the output:

21356797

13246785

31325974

45689413

34512340

56756777

how many items do you want to buy?: 1
enter a GTIN code: 21356797
>>>

which is what i want. However once i put in OR in my while loop, i can't get it to work like the first part:

while ig!=("21356797" or "13246785"):
            print("incorrect")
            ig=input("enter a GTIN code: ")
            count =count+1

and this is the output:

how many items do you want to buy?: 1
enter a GTIN code: 13246785
incorrect
enter a GTIN code: 21356797
>>>

Maybe `while ig!=("21356797" or "13246785"):` => `while not ig in ["21356797", "13246785"]:` Using `or` between 2 strings doesn't really make sense since strings are not Boolean values (although they can be coerced to such, which isn't really what you want). — John Coleman, Dec 31 '16 at 17:25
`"21356797" or "13246785"` is "21356797", look up the or operator in python. You have to do `ig != ... or ig != ...` — Jasper, Dec 31 '16 at 17:27
@Jasper: You need to `and` the conditions together, not `or` them, if you're using `!=`. Otherwise, nothing ever passes, since it will be unequal to one of the values all the time. — ShadowRanger, Dec 31 '16 at 17:31
Possible duplicate of [How do I test one variable against multiple values?](http://stackoverflow.com/questions/15112125/how-do-i-test-one-variable-against-multiple-values) — DeepSpace, Dec 31 '16 at 17:35

score 2 · Accepted Answer · answered Dec 31 '16 at 17:28

Your test:

ig!=("21356797" or "13246785")

evaluates the or condition first, returning the first "truthy" value. As such, it's exactly equivalent to:

ig!= "21356797"

since "21356797" is truthy.

You want a containment test:

ig not in ("21356797", "13246785")

or two sequential != tests and-ed together:

ig != "21356797" and ig != "13246785"
# Equivalent to:
not (ig == "21356797" or ig == "13246785")

The containment test scales to a larger set of values more cleanly, and as long as all the values are string literals, will be equally efficient (CPython caches the constant tuple of literals).

why is or not working for me in python?

1 Answers1