Actually, even if the argument (3 in this case) were an index, I would expect it to be the index of the first element _not_ to fetch, like how intervals typical

Actually, even if the argument (3 in this case) were an index, I would expect it to be the index of the first element _not_ to fetch, like how intervals typically are written with an inclusive lower bound and an exclusive upper bound as in "2 ≤ i < 13" [0]. That would make the result you're getting consistent with zero-indexing, but not with one-indexing. Of course, I don't know what Pandas is like outside this particular example, or what Pandas even is. A database thing? [0] https://www.cs.utexas.edu/users/EWD/ewd08xx/EWD831.PDF https://www.cs.utexas.edu/users/EWD/ewd08xx/EWD831.PDF