[Numpy-discussion] "expected a single-segment buffer object"
Anne Archibald
peridot.faceted@gmail....
Wed Jul 9 18:55:10 CDT 2008
Hi,
When trying to construct an ndarray, I sometimes run into the
more-or-less mystifying error "expected a single-segment buffer
object":
Out[54]: (0, 16, 8)
In [55]: A=np.zeros(2); A=A[np.newaxis,...];
np.ndarray(strides=A.strides,shape=A.shape,buffer=A,dtype=A.dtype)
---------------------------------------------------------------------------
<type 'exceptions.TypeError'> Traceback (most recent call last)
/home/peridot/<ipython console> in <module>()
<type 'exceptions.TypeError'>: expected a single-segment buffer object
In [56]: A.strides
Out[56]: (0, 8)
That is, when I try to construct an ndarray based on an array with a
zero stride, I get this mystifying error. Zero-strided arrays appear
naturally when one uses newaxis, but they are valuable in their own
right (for example for broadcasting purposes). So it's a bit awkward
to have this error appearing when one tries to feed them to
ndarray.__new__ as a buffer. I can, I think, work around it by
removing all axes with stride zero:
def bufferize(A):
idx = []
for v in A.strides:
if v==0:
idx.append(0)
else:
idx.append(slice(None,None,None))
return A[tuple(idx)]
Is there any reason for this restriction?
Thanks,
Anne
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