Reason 1: Because they make code easier to read. Purely subjective. I strongly disagree; Ruby is more concise, and ivar access is clearly seperate from method calls.

Reason 2: Because Python will allow you to "cast" self to a superclass to grant explicit access to its variables. Ruby doesn't have this problem.

Reason 3: Because Python would rather overload the keyword "self" than allocate a sigil (@).