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Python Python Basics (2015) Letter Game App Even or Odd Loop

Anders Axelsen
Anders Axelsen
3,471 Points
Posted by Anders Axelsen
Anders Axelsen
3,471 Points

Task 3: why do I get this unusual kind of error message?

This is a common error message I get: http://imgur.com/a/9OALU

I tried making the (num) correspond to even_odd(num). Is it because I am logged in in two different browsers?

  • Can you specify a problem in my code?

I have had this problem for two days now. :-) Any help would be greatly appreciated.

Kindly, Anders

even.py 
import random
start = 5
def even_odd(num):
    # If % 2 is 0, the number is even.
    # Since 0 is falsey, we have to invert it with not.
    return not num % 2

while start > 0:
    num = random.randint(1, 99)
    if even_odd(num):
        print("{} is even".format(num))
    else:
        print("{} is odd".format(num))

start -= 1

1 Answer

Jennifer Nordell
seal-mask
STAFF
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher
Jennifer Nordell
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher

Hi there! The reason there is a "communication problem" is because you've created an infinite loop. You state that it should run while start is greater than 0. To be honest, this could be abbreviated to while(start): as start will become "falsey" when it hits a value of 0. But the problem here is the decrement. The decrement doesn't happen until after the loop completes which means that start will always be 5 and the loop never ceases execution. To fix this, indent your decrement of start inside your while loop.

Hope this helps! :sparkles:

Anders Axelsen
Anders Axelsen
3,471 Points
Anders Axelsen
Anders Axelsen
3,471 Points

Hi Jennifer

First off. I actually learned a lot, being stuck on this one. And then; your explanation made perfect sense. I think, I am getting a hang of this loopy side of business.

Hopefully, I won't be initiating any black holes in the near future!

Thanks for the explanation.

ryan smith
ryan smith
687 Points

Why can't it be 

while start True:
Jennifer Nordell
seal-mask
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher
Jennifer Nordell
.a{fill-rule:evenodd;}techdegree
Jennifer Nordell
Treehouse Teacher

Hi Ryan! It's because that's not valid syntax. It needs an evaluation here. Now, you could do something like:

while start == True:

But that won't quite work with the given code either. It's comparing against an explicit value of True instead of a "truthy" value. The number 5 is "truthy", but it's not exactly the same as True.

However, if you wanted to make the condition really short, you could do what I did.

while start:

This says continue doing this loop until start is no longer "truthy". Given that 0 is a "falsey" value, the loop will cease execution when start runs down to 0.

Hope this helps! :sparkles: