What is sorting by key?

Question

Programming

Hello everyone
, I'm slowly learning programming, I ran into such a probably funny question. What is sorting by key. I watched \ tried \ read but the clarity in general did not increase in my head, only questions. Plz explain on your fingers, as for Pinocchio
Thanks
p / s questions were generated just by this article - https://habrahabr.ru/post/138535/
does not work for me, says that <<'str'['int'm' list'] object is not callable>>

Answer 1

Simply put, this is the rule by which the array is sorted.
A set of implemented comparator interfaces.