Feature suggestion: sum() ought to use a compensated summation algorithm

[Szabolcs Horvát]

Gabriel Genellina wrote:
> 
> Python doesn't require __add__ to be associative, so this should not be used as a general sum replacement.

It does not _require_ this, but using an __add__ that is not commutative 
and associative, or has side effects, would qualify as a serious misuse, 
anyway.  So I think that this isn't a real disadvantage (it can always 
be documented that sum() expects __add__ to have these properties).

But you are right that summing floats with a requirement of high 
precision is a quite specific use case, so there are no serious 
arguments to do this, either.