[SciPy-dev] array dtypechar wrong or not
pearu at scipy.org
Tue Oct 25 13:24:47 CDT 2005
On Tue, 25 Oct 2005, Travis Oliphant wrote:
> Pearu Peterson wrote:
>> Note that
>> In : array(array([1,2],dtype='I'),dtype='L').dtypechar
>> Out: 'I'
>> In : array(array([1,2],dtype='L'),dtype='I').dtypechar
>> Out: 'L'
>> I have expected 'L' and 'I', respectively. It this a bug?
> It's not really a bug, Basically, on your platform 'I' and 'L' are
> equivalent types, and so conversion is not done. I suppose that the
> typenumber could change, though, instead of doing nothing.
> Basically, it's the code in array_fromarray. Because 'I' and 'L' are
> equivalent types on your platform, only an INCREF is done. If we
> change the typecode as well as INCREF, then the original array would be
> changed, which might be surprising as well:
> a = array([1,2],dtype='I')
> b = array(a,dtype='L')
> b will point to a. If we change b to have typecode 'L', then a will
> also change. This would be surprising, I think.
I agree with you up to a point that by default array should make a copy.
Changing `b` should not change `a`, so why should `a` change on changing
`b` typecode anyway? As it is now, array does not perform a complete
copy, that is, it ignores dtype argument.
In practical application this issue doesn't matter much probably. I
noticed this behaviour and was forced to add some extra hooks to deal
with this behavior for f2py unittests that I am implementing now.
I am not requesting to change the current behavior. I am just pointing out
an unexpected behaviour. If there is no obvious way to change
this, then nevermind, but if there is, then that would be good.
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