> (n - 1)

It's also funny that one would write their own standard deviation function and include Bessel's correction. Usually if I'm manually re-implementing a standard deviation function it's because I'm afraid the implementors blindly applied the correction without considering whether or not it's actually meaningful for the given analysis. At the very least, the correct name for what's implemented there should really be `sample_std_dev`.

It is sadly really inconsistent. The stdlib statistics has two separate functions, stdev for sample and pstdev for population. Numpy and pandas both have .std() with ddof (delta degrees of freedom) as a parameter, but numpy defaults to 0 (population) and pandas to 1 (sample).