byteswap problem

[mshemuni]

I'm not sure if this is the place to write the issue.

I am using Linux Mint 18 and tested this problem with both Ubuntu 14.04 and 16.04 and all were 64bit systems. Sorry I have some modules and methods so there's no point to share the whole code but basically I read fits file like:

from astropy.io import fits as fts

hdu = fts.open(src, mode='readonly')
data = hdu[0].data 

then I pass the data to sep as below:

from sep import Background, extrac
from numpy import asarray as ar

bkg = Background(data)
data_sub = data - bkg
all_objects = ar(extract(data_sub, 1.5, err=bkg.globalrms))
all_objects = all_objects[all_objects['flag'] == 0]

at line bkg = Background(data) error below occurs:

valueerror: input array with dtype '>f4' has non-native byte order. only native byte order arrays are supported. to change the byte order of the array 'data', do 'data = data.byteswap().newbyteorder()'

I added the line data = data.byteswap().newbyteorder(). Nothing changed. I had the same problem. With and without the suggested line.

I figured it out. The data returned by astropy has dtype=float32. And I just changed dtype by float64 as shown below and everything was ok.

data = data.astype(np.float64)

I think I must be able to use 32bit data type in a 64bit system.

[kbarbary]

You're right that you should be able to use float32 on a 64-bit processor. A common misunderstanding about 32-bit versus 64-bit processors is that "32" and "64" refer only to the native integer size, but doesn't have anything to do with floating point numbers. Both types of processors have both native 32-bit and 64-bit floating point units.

data = data.astype(np.float64) likely converts to the native endianness (little endian), so that's why it worked.

After doing data = data.byteswap().newbyteorder() and before passing data to any SEP function, data.dtype should be dtype('<f4'). Can you check this?

[mshemuni]

I took a look to dtype and it says: float64.