local variable 'juveniles' referenced before assignment

[Chris Angelico]

On Wed, Jan 13, 2016 at 11:23 PM, Alan Robinson
<arobinson at lordlawson.org.uk> wrote:
> def menu():
>     option = int(input("Please select an option: \n 1: Set Generation 0 Values \n 2: View Generation 0 Values \n 3: Run Model \n 4: Print values"))
>
>     if option == 1:
>         juveniles,adults,seniles = setGen()
>     elif option == 2:
>         displayGen()
>     elif option == 3:
>         runModel(juveniles,adults,seniles)
>     elif option == 4:
>         print(juveniles,adults,seniles)
>     menu()
>

This is a classic use of recursion instead of iteration. When you call
menu() again, you're creating a completely new 'slot' for the new
function; it has its own set of names. Assigning to names in one call
of menu() has no effect on any other call.

Instead, look into the way a while loop works. You'll find that your
code is simpler and clearer, plus your variables will stay set.

ChrisA