Love it.

The single-line if statement syntax used here is an elegant way of including both a null check and it's corresponding if-block statement.

What is the meaning of the symbol * here?

If your browser is showing the spirals using a narrow font, it may be more difficult to see the spiral pattern at first glance. The spiral pattern may be easier to see when visually spread out more:

0 0 0 0 0 0 0 0 0 0 
. . . . . . . . . 0 
0 0 0 0 0 0 0 0 . 0 
0 . . . . . . 0 . 0 
0 . 0 0 0 0 . 0 . 0 
0 . 0 . . 0 . 0 . 0 
0 . 0 . . . . 0 . 0 
0 . 0 0 0 0 0 0 . 0 
0 . . . . . . . . 0 
0 0 0 0 0 0 0 0 0 0 

You know when you see something so simple.
And it makes so much sense.
And you missed it when you were solving the problem.

This is that 🤦‍♂️

Nice kata.

I'm not sure if there's a name for it. I'm using it here because otherwise int('') would throw an error, but '' also evaluates to false, so using or here lets me coerce '' to 0.

Interesting to see the OR operator in the argument to int()
ie. int(a OR b)

What is this technique called? I've not seen it described anywhere and can't seem to find a name for it.

Thanks for posting. I had the same mistake.