[AstroPy] question on saving fits files

[Marcio Melendez]

The problem is that you just changed a variable, dt, and not your object
hdu (the one that you are writing to). So you need to replace dt = dt*1000
with hdu.data = dt*1000. Alternatively you can create another object (if
you want to keep hdu intact) by:

hdu_new = pyfits.PrimaryHDU(dt) # where dt = hdu.data*1000
hdu_new.writeto('small_mod.fits')

Remember to add clobber = True to your writeto if you want to overwrite the
file.

I hope this help,

On Wed, Feb 10, 2016 at 11:42 AM, Doug Burke <dburke.gw at gmail.com> wrote:

>
> Grigoris,
>
> If you change 'dt = dt * 1000' to 'dt *= 1000' do you get what you expect?
>
> Doug
>
> On Wed, Feb 10, 2016 at 11:30 AM Grigoris Maravelias <
> gr.maravelias at gmail.com> wrote:
>
>> Hello!
>>
>> I have a problem with a rather simple process, but I cannot understand
>> what I am doing wrong. I have an image in a fits file that i want to
>> open and process its data values, and save it as another file (including
>> some extra information on the header for what I did). So according to
>> the astropy docs [1] I did the following:
>>
>> hdulist = fits.open('small.fits')
>> hdu = hdulist[0]
>> hd = hdu.header
>> dt = hdu.data
>>
>> hd.append(('HISTORY', 'blabla '), bottom=True)
>>
>> print dt            # check data before
>> dt = dt*1000
>> print dt            # and after
>>
>> hdulist.writeto('small_mod.fits')
>>
>> If I print dt before and after their modification (multiplied by 1000) I
>> can see that they are indeed different (properly multiplied), but when I
>> save the fits file I just see the original data values (however, the
>> HISTORY line is added properly in the primary header).
>>
>> What am I missing here?
>>
>> Best
>> Grigoris
>>
>>
>> [1] http://docs.astropy.org/en/stable/io/fits/usage/headers.html
>>
>>
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>>
>
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>


-- 
Marcio B. Melendez, Ph.D
JWST ISIM Optics Support Scientist
Wyle Science, Technology and Engineering Group
NASA Goddard Space Flight Center  Greenbelt, MD  20771
Bldg. 29 Rm. T29-10, phone: 301-286-8517
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