Steven D'Aprano <steve+pyt...@pearwood.info> added the comment:

TL;DR: I'm not likely to accept this feature request without at least one of 
(1) a practical use-case, (2) prior art in other statistics software, or (3) a 
strong mathematical justification for why this is meaningful and useful.


I'm not categorically against this idea, but it seems a bit fishy to me. If you 
have no data, how do you know what default value to give that would be 
appropriate for your (non-existent) observations?

It might help if you could show a real-life example of how, and why, you would 
use this, and how you would choose the default?

Another possibility would be to find prior-art: another language, library or 
stats calculator which already offers this feature.

Alternatively, a mathematical/statistical justification for a default. For 
example, the empty sum is normally taken as 0 and the empty product as 1. R 
returns either a NAN or NA for the empty mean (depending on precisely how you 
calculate it).

While I'm personally sympathetic to the nuisance factor of having to wrap code 
in try...except blocks (my *personal* preference would have been for mean to 
return NAN on empty input) I think you will need to make a stronger case than 
just the analogy with min and max.

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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue39094>
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