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Date: Fri, 28 Feb 2014 08:52:48 +1100
Subject: Re: Tuples and immutability
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
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Xref: csiph.com comp.lang.python:67168

On Fri, Feb 28, 2014 at 8:47 AM, Nick Timkovich <prometheus235@gmail.com> wrote:
> On Thu, Feb 27, 2014 at 10:33 AM, Chris Angelico <rosuav@gmail.com> wrote:
>>
>> On Fri, Feb 28, 2014 at 3:27 AM, Eric Jacoboni <eric.jacoboni@gmail.com>
>> wrote:
>> > But, imho, it's far from being a intuitive result, to say the least.
>>
>> It's unintuitive, but it's a consequence of the way += is defined. If
>> you don't want assignment, don't use assignment :)
>>
>> ChrisA
>
>
> Where is `.__iadd__()` called outside of `list += X`?  If the only
> difference from `.extend()` is that it returns `self`, but the list was
> already modified anyway, why bother with reassignment?

Not everything handles += that way. You can't mutate the integer 5
into 7 because someone had 5 in x and wrote "x += 2". So it has to
reassign.

Actually, integers just don't define __iadd__, but the principle applies.

ChrisA