[Numpy-discussion] Regression: in-place operations (possibly intentional)

Nathaniel Smith njs@pobox....
Fri Sep 21 17:20:30 CDT 2012


On Fri, Sep 21, 2012 at 10:04 PM, Chris Barker <chris.barker@noaa.gov> wrote:
> On Fri, Sep 21, 2012 at 10:03 AM, Nathaniel Smith <njs@pobox.com> wrote:
>
>> You're right of course. What I meant is that
>>   a += b
>> should produce the same result as
>>   a[...] = a + b
>>
>> If we change the casting rule for the first one but not the second, though,
>> then these will produce different results if a is integer and b is float:
>
> I certainly agree that we would want that, however, numpy still needs
> to deal tih pyton symantics, which means that wile (at the numpy
> level) we can control what "a[...] =" means, and we can control what
> "a + b" produces, we can't change what "a + b" means depending on the
> context of the left hand side.
>
> that means we need to do the casting at the assignment stage, which I
> gues is your point -- so:
>
> a_int += a_float
>
> should do the addition with the "regular" casting rules, then cast to
> an int after doing that.
>
> not sure the implimentation details.

Yes, that seems to be what happens.

In [1]: a = np.arange(3)

In [2]: a *= 1.5

In [3]: a
Out[3]: array([0, 1, 3])

But still, the question is, can and should we tighten up the
assignment casting rules to same_kind or similar?

-n


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