[Python-Dev] Behaviour of max() and min() with equal keys (original) (raw)

Matthew Woodcraft matthew at woodcraft.me.uk
Tue Sep 7 23:07:35 CEST 2010

Mark Dickinson wrote:

Matthew Woodcraft wrote:

In CPython, the builtin max() and min() have the property that if there are items with equal keys, the first item is returned. From a quick look at their source, I think this is true for Jython and IronPython too.

It's actually not clear to me that this behaviour is ideal; it might make more sense to have max() return the first item among equal largest elements, and min() return the last item.

I don't care a great deal what the behaviour is; I would like it to be consistent across Python versions, and I think the pragmatic way to achieve that is to document the current behaviour.

Can you give examples of code that relies on max and min returning the first among equals?

An existing regression test whose output depends on which choice is made.

(I was writing some code today which had to duplicate the behaviour of a non-Python program which uses first-among-equals, which is what brought this question up. In that case I wouldn't think it unreasonable to have to hand-code the loop rather than using max(), but if in practice Python is always going to be first-among-equals, it seems to me we might as well be 'allowed' to take advantage of it.)

-M-

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