10000 printing fits_header attribute of Map object causes ValueError exception if metadata values include comments · Issue #7926 · sunpy/sunpy · GitHub
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printing fits_header attribute of Map object causes ValueError exception if metadata values include comments #7926

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jslavin opened this issue Dec 11, 2024 · 3 comments
Open

printing fits_header attribute of Map object causes ValueError exception if metadata values include comments #7926

jslavin opened this issue Dec 11, 2024 · 3 comments
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Discussion An issue opened for, or undergoing discussion. map Affects the map submodule

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@jslavin
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jslavin commented Dec 11, 2024 •
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Describe the bug

I've been trying to add values with comments to the metadata of a Sunpy map. I can create the map with the metadata with comments, e.g. mdata['value'] = (42, 'meaning of life'). And if I print them it looks right, roughly, printing as ('value', (42, 'meaning of life')). However if I try to do mmap.fits_header, I get an error:
ValueError: Illegal value: (42, 'meaning of life')
which is actually raised by astropy/io/fits/card.py (which is called in sunpy/io/_fits.py

To Reproduce

import sunpy

mmap = sunpy.map.Map(fits_file)
mdata = mmap.meta
mdata['value'] = (42, 'meaning of life')
mmap2 = sunpy.map.Map(mmap.data, mdata)
mmap2.fits_header
@jslavin
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jslavin commented Dec 11, 2024

It appears that Map metadata doesn't support comments. If I create a map object from data and a fits header object that has comments for some of its keywords, the comments just get dropped in the map metadata.

@Cadair
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Cadair commented Dec 11, 2024

This is just a quick drive-by from my phone, but I am pretty sure sunpy meta doesn't support the = (value, comment) syntax like astropy. I think you need to edit the key comments dict (I can't remember exactly where that is)

@nabobalis nabobalis added map Affects the map submodule Discussion An issue opened for, or undergoing discussion. labels Dec 11, 2024
@jslavin
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jslavin commented Dec 13, 2024

Yes, I found a way to add comments to the metadata. You have to add items to the 'keycomments' dictionary:
mmap = sunpy.map.Map(fits_file)
mdata = mmap.meta
mdata["value"] = 42
mdata['keycomments"]["value"] = "meaning of life"

Whether doing that could/should be made simpler is something that could be discussed.

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