Confusion with unpacking in python

Question

This is basically a code golf problem I was solving. The statement goes like so:

Given N, X and a line with X numbers between 0 and 9. Print all valid numbers between 0 and N inclusive. A number is valid if all of your digits are in line. If the sequence is empty, print NONE.

And this was my first attempt:

    n,x=map(int,input().split())
    d=set(input().split())
    print(*[v for v in range(n+1)if not set(str(v)).difference(d)]or'NONE')

Why does python unpack the string 'NONE' here? Isn't this supposed to be a simple short circuit where python prints the unpacked list if it is not empty or otherwise print the full string intact?

Answer 1

If you try a simpler example, e.g.:

print(*[] or 'Test')

you'll see:

T e s t

It's because the call is actually parsed as:

print(*([] or 'Test'))

Due to precedence rules. Otherwise, the expression print((*[]) or 'Test') wouldn't even make any sense. Instead, try:

print(*[] or ['Test'])

and that will work like you expected.