Python inherits this from Perl, where it's called elsif.
In Python's case, else if as two separate constructs like it is in C-like languages would be quite ugly as you'd have to have else: if: with two indenting levels.
It's arguable whether special-casing the two keywords together would be better (so making else if a single construct, like the not in operator.
PL/SQL also has elsif, and the C preprocessor has it spelled elif.
