actually there is: "... ordered by the members id" - check description

You need order the results ascending and then it works because the expected results are ordered as well. It shouldn't be like this cuz there is nothing about ordering the results in the instructions

WTF! SPOILER FLAG!! X/

and for your question, there are more cons than pros to the default argument here, because a user can accidentally mess with your function if it's not documented. Other than that, there is no real difference, I'd say (since there is no tail call optimization in python, afaik).

you can do that all you want, you'll just have a solution that either times out or exhausts all its allocated memory. You'd bet that if something like that could cause troubles, CW would already have been down years ago... x)