Python using `!=`, `or` and `while`

Question

For example, I want to run the loop when choice isn't neither1 nor 2. So my code is like this:

choice = int(input('Enter a number: '))

while choice != 1 or choice != 2:
    # some code here

Now here is my question, whatever choice is 1, 2, or other, this loop will still run because choice can't be 1 and 2 at once. And I don't know why does this also don't work:

while choice != 1 or 2:
    # some code here

I'm sorry if this is a duplicate.

score 2 · Accepted Answer · answered Sep 29 '15 at 04:10

2

The issue is that you are using or , you have to use and since you want to check that choice is not 1 and choice is not 2 either. Example -

while choice != 1 and choice != 2:

answered Sep 29 '15 at 04:10

Anand S Kumar

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hah it must be late ... some how it completely escaped me that he should be using and :P – Joran Beasley Sep 29 '15 at 04:16

score 1 · Answer 2 · answered Sep 29 '15 at 04:10

1

Every number is either not 1 or not 2. What you want is for it to be not 1 and not 2. So do while choice != 1 and choice != 2.

You can also do while choice not in (1, 2), which is more easily extensible to a larger set of values to check against.

answered Sep 29 '15 at 04:10

BrenBarn

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score 1 · Answer 3 · answered Sep 29 '15 at 04:11

1

while choice not in [1,2]:

or

while choice != 1 or choice != 2:

the problem is

while choice != 1 or 2:

is evaluated left to right so pretend choice = 3

while 3 != 1 or 2: = > while (3 != 1) or 2: ==> while (False) or 2: =>> 2 is always true so it doesnt work

answered Sep 29 '15 at 04:11

Joran Beasley

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The second code line is exactly the same as in the code in Question. And it will not work. – Psytho Sep 29 '15 at 07:36

Python using `!=`, `or` and `while`

3 Answers3

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