[Python-ideas] Re: NAN handling in statistics functions

Returning a NaN by default has the advantage of being consistent with IEEE 754 semantics for sequence-based operations (like `sum` and `dot`) and with existing Python `math` module functions like `fsum`, `prod` and `hypot`. In IEEE 754, the majority of operations silently return a NaN (not signalling any floating-point exception) when given a NaN as input.