The scalar indexers, .iat and .at, only accept scalar values. They fail if anything else is passed to them. They are drop-in replacements for .iloc and .loc when doing scalar selection. The timeit magic command times entire blocks of code when preceded by two percentage signs and a single time when preceded by one percentage sign. It shows that about 2.5 microseconds are saved on average by switching to the scalar indexers. This might not be much but can add up quickly if scalar selection is repeatedly done in a program.