Proposal: min(None, x) and max(None, x) return x

[Andrew Koenig]

Eric> So I told myself: wouldn't it be great if max(None, x) or
Eric> min(None, x) always simply returned x?

My first thought was that this was an excellent idea.

Then I thought again.

Here's the problem:  The notion that max(None, x) and min(None, x)
should both return x is one of three desirable properties that cannot
all be true at once.  Here are the other two:

        1) Whenever x < y, min(x, y) is x and max(x, y) is y.

        2) < is an order relation over all types.

The desirability of (1) should be obvious.  (2) is more subtle, but
it is necessary for it to be possible to sort a vector of heterogenously
typed objects.

Now, if max(None, x) and min(None, x) both yield x, and (1) is true,
then x > None and x < None must both be true.  But then (2) cannot
be true.

So the cost of your proposal would be either to break the consistency
between max/min and >/<, or to render unsortable vectors of values
that include None.

I don't think it's worth it.


-- 
Andrew Koenig, ark at research.att.com, http://www.research.att.com/info/ark