[Numpy-discussion] Contiguity of result of astype changed - intentional?
Matthew Brett
matthew.brett@gmail....
Wed Sep 12 13:36:10 CDT 2012
Hi,
We hit a subtle behavior change for the ``astype`` array method
between 1.6.1 and 1.7.0 beta.
In 1.6.1:
In [18]: a = np.arange(24).reshape((2, 3, 4)).transpose((1, 2, 0))
In [19]: a.flags
Out[19]:
C_CONTIGUOUS : False
F_CONTIGUOUS : False
OWNDATA : False
WRITEABLE : True
ALIGNED : True
UPDATEIFCOPY : False
In [20]: b = a.astype(float)
In [21]: b.flags
Out[21]:
C_CONTIGUOUS : True
F_CONTIGUOUS : False
OWNDATA : True
WRITEABLE : True
ALIGNED : True
UPDATEIFCOPY : False
In [22]: b.strides
Out[22]: (64, 16, 8)
So - ``a.astype(float)`` here has made a new C-contiguous array,
somewhat as implied by the 'copy' explanation in the docstring. In
1.7.0 beta, ``a`` is the same but:
In [22]: b.flags
Out[22]:
C_CONTIGUOUS : False
F_CONTIGUOUS : False
OWNDATA : True
WRITEABLE : True
ALIGNED : True
UPDATEIFCOPY : False
In [23]: b.strides
Out[23]: (32, 8, 96)
Is this intended? Is there a performance reason to keep the same
strides in 1.7.0?
Thanks for any pointers,
Matthew
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