On Wed, 17 Oct 2007 13:41:06 +0200, Hrvoje Niksic wrote:
> Duncan Booth <[EMAIL PROTECTED]> writes:
>
>> Hrvoje Niksic <[EMAIL PROTECTED]> wrote:
>>
>>> I've recently been bitten by [rebinding the var to what __iadd__
>>> returns], and I don't understand the reasoning behind __iadd__'s
>>> design. I mean, what is the point of an *in-place* add operation
>>> (and others) if it doesn't always work in-place?
>>>
>> A very common use case is using it to increment a number:
>
> I'm aware of that; but remember that there's still __add__. It would
> be sufficient for numbers not to implement __iadd__. And, in fact,
> they already don't:
>
>>>> 1 .__add__(1)
> 2
>>>> 1 .__iadd__(1)
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> AttributeError: 'int' object has no attribute '__iadd__'
>
> The current implementation of += uses __add__ for addition and
> __iadd__ for addition that may or may not be in-place. I'd like to
> know the rationale for that design.
Simply not to introduce special cases I guess. If you write ``x.a += b``
then `x.a` will be rebound whether an `a.__iadd__()` exists or not.
Otherwise one would get interesting subtle differences with properties for
example. If `x.a` is a property that checks if the value satisfies some
constraints ``x.a += b`` would trigger the set method only if there is no
`__iadd__()` involved if there's no rebinding.
Ciao,
Marc 'BlackJack' Rintsch
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