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Date: Thu, 4 Dec 2014 21:18:46 +1100
Subject: Re: How is max supposed to work, especially key.
From: Chris Angelico <rosuav@gmail.com>
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On Thu, Dec 4, 2014 at 9:09 PM, Albert van der Horst
<albert@spenarnc.xs4all.nl> wrote:
>>If there is more than one item with the maximum calculated the first is
>>given, so for your attempt
>>
>>max(xrange(100,200), key=lambda i: i%17==0 )
>
>>
>>the values False, False, True, False, ... are calculated and because
>>
>>>>> True > False
>>True
>>
>>the first one with a True result is returned.
>>
>
> So in that case max doesn't return the maximum (True), but instead
> something else.
>
> Useful as that function may be, it shouldn't have been called max.
>
> I don't blame myself for being misled.

If lots of them are equally the largest, by whatever definition of
largest you have, it has to do one of three things:

1) Raise an exception
2) Return multiple items (either as a tuple, or a generator, or something)
3) Pick one of them and return it.

Python's max() does the third, and for the picking part, uses the
first one it comes across - a decent way to do it.

If there's no clear maximum, it can't do any better than that. It's
still returning something for which there is no greater.

ChrisA