I think it's a testimony to the readability of Python that I've never even programed in the language, nor am I familiar with the finer points of the list syntax

I think it's a testimony to the readability of Python that I've never even programed in the language, nor am I familiar with the finer points of the list syntax (a[::2]?!), and yet this mucked up piece of shit nonetheless gave me the first impression of a prime number sieve. I actually still don't understand how the sieve works, but it somehow just looks like one. Or is it just the case that assuming every obfuscated loop is a prime number sieve is disproportionately likely to be true?