El dj 26 de 04 del 2007 a les 11:38 -0700, en/na Russell E. Owen va escriure:

In converting some code from numarray to numpy I had this: isBigendian = (arr.isbyteswapped() != numarray.isBigEndian)

The only numpy version I've come up with is: isBigEndian = (arr.dtype.descr[0][1][0] == '>')

isBigEndian = (arr.dtype.str[0] == '>') is a little bit shorter. A more elegant approach could be: isBigEndian = arr.dtype.isnative ^ numpy.little_endian Cheers, -- Francesc Altet | Be careful about using the following code -- Carabos Coop. V. | I've only proven that it works, www.carabos.com | I haven't tested it. -- Donald Knuth

In article <4630FDD9.9030307@ieee.org>, Travis Oliphant <oliphant.travis@ieee.org> wrote:

Russell E. Owen asked how best to translate some numarray code that determines if an array is in big-endian order...

What are you trying to test for (where a data-type is big-endian or not?).

I really want to know if the array is in big-endian order (I don't care whether it's native). This is for sending arrays to the ds9 image viewer via xpa (and communicating with ds9 is not easy). To do this reliably I need to indicate the byte order of the data. I suppose there are alternatives such as making a "native byte order" copy of the data and sending that without any flag. But I think it's easier to just send the flag.

To directly answer your question, however.

On page 42 of the sample pages (online for free) of my book, the recommended translation of numarray's arr.isbyteswapped() is (not arr.dtype.isnative)

I found that (I own your book).

The translation of numarray.isBigEndian is (not numpy.little_endian)

I missed that one (and I did look for it).

... isBigEndian = arr.dtype.isnative ^ numpy.little_endian

That should be much clearer than my translation. Thanks! -- Russell

Russell, This should work as a consistent test for bigendian: -> isBigEndian = (obj.dtype.str[0] == '>') Also, I have ported numarray's numdisplay to numpy if you would like to directly display an array in DS9. We haven't done an official release yet (sometime soon) but I can forward you a copy if you are interested. Chris

On Thu, Apr 26, 2007 at 05:22:42PM -0400, Christopher Hanley wrote:

This should work as a consistent test for bigendian:

-> isBigEndian = (obj.dtype.str[0] == '>')

Is this test always safe, even on big endian machines? Couldn't the dtype.str[0] sometimes be '='? Regards Stéfan

On Fri, Apr 27, 2007 at 08:49:16AM -0400, Christopher Hanley wrote:

...

...

-> isBigEndian = (obj.dtype.str[0] == '>')

Is this test always safe, even on big endian machines? Couldn't the dtype.str[0] sometimes be '='?

The test does would on big endian machines. What wouldn't work would be something like this:

-> isBigEndian = (obj.dtype.byteorder == '>')

On a big-endian machine you would get '=' in this case.

Ah, yes, I was confused. What I meant to ask was, couldn't dtype.str[0] sometimes be '|'? Cheers Stéfan

In article <46311822.2010206@stsci.edu>, Christopher Hanley <chanley@stsci.edu> wrote:

Russell,

This should work as a consistent test for bigendian:

-> isBigEndian = (obj.dtype.str[0] == '>')

Also, I have ported numarray's numdisplay to numpy if you would like to directly display an array in DS9. We haven't done an official release yet (sometime soon) but I can forward you a copy if you are interested.

I would very much like a copy. I've never heard of numdisplay before but am always interested in code that can talk to DS9. I'm porting RO.DS9. it works but has some rather ugly bits of code in it to deal with the many vagaries of xpa and ds9. -- Russell

On 4/27/07, Christopher Barker <Chris.Barker@noaa.gov> wrote:

Is there really no single method to call on an ndarray that asks: "what endian are you"

I know not every two-liner should be made into a convenience method, but this seems like a good candidate to me.

+1 I came across this source of minor confusion and excess code lines when writing the matlab io module for scipy. dtype.isbigendian? Matthew