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From: Rob Williscroft <rtw@rtw.me.uk>
Subject: Re: None versus MISSING sentinel -- request for design feedback
Date: Fri, 15 Jul 2011 07:43:57 +0000 (UTC)
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Steven D'Aprano wrote in news:4e1fd009$0$29986$c3e8da3
$5496439d@news.astraweb.com in gmane.comp.python.general:

> I'm designing an API for some lightweight calculator-like statistics
> functions, such as mean, standard deviation, etc., and I want to support
> missing values. Missing values should be just ignored. E.g.:
> 
> mean([1, 2, MISSING, 3]) => 6/3 = 2 rather than 6/4 or raising an error.

If you can't make your mind up then maybe you shouldn't:

MISSING = MissingObject()
def mean( sequence, missing = MISSING ):
  ...

Rob.