Hi, I have a (UInt16) 3d data stack and want to get to it's underlying buffer (to (later) feed it into memmap) ... I noticed that len(pr2._flat) is half of len(pr2._data) - like it doesn't multiply itemsize in.
pr2.shape (40, 512, 512) pr2.flat.shape (10485760) 512*512*40 10485760 len(pr2.flat) 10485760 pr2.flat._itemsize 2 len(pr2._data) 20971520 pr2._byteoffset 0
Is this a bug or am I missunderstanding ? Thanks, Sebastian Haase
On Wed, 2004-10-27 at 12:58, Sebastian Haase wrote:
Hi, I have a (UInt16) 3d data stack and want to get to it's underlying buffer (to (later) feed it into memmap) ... I noticed that len(pr2._flat) is half of len(pr2._data) - like it doesn't multiply itemsize in.
pr2.shape (40, 512, 512) pr2.flat.shape (10485760) 512*512*40 10485760 len(pr2.flat) 10485760 pr2.flat._itemsize 2 len(pr2._data) 20971520 pr2._byteoffset 0
Is this a bug
No.
or am I missunderstanding ?
Yes. _data is "an object which supports the buffer protocol". In this context, it is effectively a string and thus the product of the total number of elements and the itemsize. (We'll ignore for now the fact that not every array uses the entire buffer.) In contrast, shape(.flat) is only the total number of elements and is independent of itemsize. Regards, Todd
Of course ! sorry I forgot. Thanks, Sebastian On Friday 29 October 2004 06:26 am, Todd Miller wrote:
On Wed, 2004-10-27 at 12:58, Sebastian Haase wrote:
Hi, I have a (UInt16) 3d data stack and want to get to it's underlying buffer (to (later) feed it into memmap) ... I noticed that len(pr2._flat) is half of len(pr2._data) - like it doesn't multiply itemsize in.
pr2.shape
(40, 512, 512)
pr2.flat.shape
(10485760)
512*512*40
10485760
len(pr2.flat)
10485760
pr2.flat._itemsize
2
len(pr2._data)
20971520
pr2._byteoffset
0
Is this a bug
No.
or am I missunderstanding ?
Yes. _data is "an object which supports the buffer protocol". In this context, it is effectively a string and thus the product of the total number of elements and the itemsize. (We'll ignore for now the fact that not every array uses the entire buffer.) In contrast, shape(.flat) is only the total number of elements and is independent of itemsize.
Regards, Todd
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participants (2)
-
Sebastian Haase -
Todd Miller