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Perhaps to align with the final "else" clause, or it was familiar to c programmers due to the c-preprocessor directive https://gcc.gnu.org/onlinedocs/cpp/Elif.html, or they were mindful that every character counts when you want to push 80 character max-line-length style?

To be clear, that's not a new feature in 3.8.

It fits in a single indent space. At least that's what my professor told us, and it seems to be confirmed by a quick online search.

Or just else if... but honestly elif is easiest to type and it's not hard to understand.

Hard is being used in a "type the keys" sense. It's more complexity to borrow idioms from languages then slightly change the syntax (PHP!), which isn't necessary. Like most languages, choices are made without evidence (but plenty of anecdotes and personal style).