OR statement handling two != clauses Python

python operator-keyword clause
thebill picture thebill · Apr 15, 2011 · Viewed 72.7k times · Source

(Using Python 2.7) I understand this is pretty elementary but why wouldn't the following statement work as written:

input = int(raw_input())
while input != 10 or input != 20:
    print 'Incorrect value, try again'
    bet = int(raw_input())

Basically I only want to accept 10 or 20 as an answer. Now, regardless of 'input', even 10, or 20, I get 'Incorrect value'. Are these clauses self conflicting? I thought that the OR statement would say OK as long as one of the clauses was correct. Thanks!

Answer

Felix Kling picture Felix Kling · Apr 15, 2011

You need and:

while input != 10 and input != 20:

Think it through: If the input is 10, then the first expression is false, causing Python to evaluate the second expression input != 20. 10 is different form 20, so this expressions evaluates to true. As false or true == true, the whole expression is true.
Same for 20.

Related questions

How do operator.itemgetter() and sort() work?

I have the following code: # initialize a = [] # create the table (name, age, job) a.append(["Nick", 30, "Doctor"]) a.append(["John", 8, "Student"]) a.append(["Paul", 22, "Car Dealer"]) a.append(["Mark", 66, "Retired"]) # sort the table by age import operator a.sort(key=…

Read More
What do >> and << mean in Python?

I notice that I can do things like 2 << 5 to get 64 and 1000 >> 2 to get 250. Also I can use >> in print: print >>obj, "Hello world" What is happening here?

Read More
Python's Logical Operator AND

I'm a little confused with the results I'm getting with the logical operators in Python. I'm a beginner and studying with the use of a few books, but they don't explain in as much detail as I'd like. here is …

Read More