Thanks all,
Now I need to try to sum this all up to present to my students. ;-)
-Chris
On Tue, May 20, 2014 at 4:56 PM, Terry Reedy <tjre...@udel.edu> wrote:
> On 5/20/2014 12:30 PM, Chris Barker wrote:
>
>> >>>> [].sort() is None
>> > True
>> >>>> "ABC".lower() is None
>> > False
>>
>
> Is there a reference anywhere as to *why* the convention in Python is to
>> do it that way?
>>
>
> In short, reducing bugs induced by mutation of aliased objects. Functional
> languages evade the problem by prohibiting mutation (sometimes at the cost
> of inefficiency).
>
> In an alternate universe, the example above might become
>
> >>> a = []; a.sort() is a
> True
> >>> a = "ABC"' a.lower() is a
> False
>
> As I suggested earlier, having pure mutation methods not return anything
> made is easy to suggest a mutation + non-self return method, list.pop. If
> all mutation methods had previously returned 'self', there might have been
> disagreement over whether the item return should augment or replace the
> self return. Before you say the latter, consider the inconsistency of only
> sometimes returning self and the potential consistency between
>
> >>> most, last = 'a b c'.rsplit(maxsplit=1)
> >>> most, last
> ('a b', 'c')
>
> >>> most, last = [0, 1, 2].pop()
> >>> most, last
> ([0, 1], 2)
>
> One could also consider first, rest pairings.
>
> --
> Terry Jan Reedy
>
>
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--
Christopher Barker, Ph.D.
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