7 years later...
I'm updating the description to be a bit less vague... at least I'm trying: https://github.com/codewars/codewars.com/issues/2545
I didn't understand the "== 1" part and why use len? can you explain it to me please?
No, these exercises are just for fun.
filter() returns an iterator. So you need to change it to list or tuple. This is for python 3.
Very Beautiful solution, I have aesthetic pleasure, when i'm looking at this, Thank u very much !
Great job MAN:)
Yes, I think you guessed right. If f is an empty filter object (list(f) == ), then in Python 3 bool(f) returns True which is why you do not get what you expected.
list(f) == 
This comment is hidden because it contains spoiler information about the solution
Third line checks if there are any columns, rows or blocks which are not a set of numbers from 1 to 9.
Second line helps define blocks.
Does this help you? You can ask more specific questions if you are missing something.
Could someone explain the idea of this solution? Thanks!