[Numpy-discussion] np.array execution path

Travis Oliphant travis@continuum...
Sat Sep 22 13:12:02 CDT 2012


Check to see if this expression is true

no is o

In the first case no and o are the same object


Travis 

--
Travis Oliphant
(on a mobile)
512-826-7480


On Sep 22, 2012, at 1:01 PM, Sebastian Berg <sebastian@sipsolutions.net> wrote:

> Hi,
> 
> I have a bit of trouble figuring this out. I would have expected
> np.asarray(array) to go through ctors, PyArray_NewFromArray, but it
> seems to me it does not, so which execution path is exactly taken here?
> The reason I am asking is that I want to figure out this behavior/bug,
> and I really am not sure which function is responsible:
> 
> In [69]: o = np.ones(3)
> 
> In [70]: no = np.asarray(o, order='C')
> 
> In [71]: no[:] = 10
> 
> In [72]: o # OK, o was changed in place:
> Out[72]: array([ 10.,  10.,  10.])
> 
> In [73]: no.flags # But no claims to own its data!
> Out[73]: 
>  C_CONTIGUOUS : True
>  F_CONTIGUOUS : True
>  OWNDATA : True
>  WRITEABLE : True
>  ALIGNED : True
>  UPDATEIFCOPY : False
> 
> In [74]: no = np.asarray(o, order='F')
> 
> In [75]: no[:] = 11
> 
> In [76]: o # Here asarray actually returned a real copy!
> Out[76]: array([ 10.,  10.,  10.])
> 
> 
> Thanks,
> 
> Sebastian
> 
> 
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