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Add support for reading compressed FITS files with UNCOMPRESSED_DATA#19363

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saimn merged 5 commits intoastropy:mainfrom
astrofrog:support-uncompressed-data
Mar 16, 2026
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Add support for reading compressed FITS files with UNCOMPRESSED_DATA#19363
saimn merged 5 commits intoastropy:mainfrom
astrofrog:support-uncompressed-data

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@astrofrog astrofrog commented Mar 6, 2026 •
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Description

This PR adds support for reading in FITS files that use the legacy UNCOMPRESSED_DATA fallback mechanism (rather than GZIP_COMPRESSED_DATA).

The fact this didn't work let two two issues which shows these files do exist in the wild:

Just to confirm, this seems to work with the file linked in #17821

Not sure if this is an enhancement or a bug fix though - what do you think @saimn?

The diff for _tiled_compression.py makes more sense if you ignore whitespace diffs

Fixes #15477
Fixes #17821

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github-actions Bot commented Mar 6, 2026

Thank you for your contribution to Astropy! 🌌 This checklist is meant to remind the package maintainers who will review this pull request of some common things to look for.

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@saimn saimn added this to the v7.2.1 milestone Mar 6, 2026
@saimn saimn added the backport-v7.2.x on-merge: backport to v7.2.x label Mar 6, 2026
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saimn commented Mar 6, 2026

Thanks, LGTM.
Probably bugfix since astropy used to read those files (and maybe even write them as suggested in a comment in one the issues?). Let's see if backport is easy, otherwise we can keep this for 8.0.

@astrofrog astrofrog added Bug and removed Bug labels Mar 6, 2026
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astrofrog commented Mar 6, 2026

I'm tempted to call it a bug fix since it is stopping people opening real FITS files. Do you agree @saimn?

@astrofrog astrofrog marked this pull request as ready for review March 6, 2026 13:36
@astrofrog astrofrog requested a review from saimn as a code owner March 6, 2026 13:36
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astrofrog commented Mar 6, 2026

@saimn - ok I've now added a bugfix changelog entry so this is ready for review. I'll try and check whether we ever supported writing but tbh I'm not sure we should since it's no longer recommended?

pllim
pllim reviewed Mar 6, 2026
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Comment thread docs/changes/io.fits/19363.bugfix.rst Outdated
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pllim commented Mar 6, 2026

@saimn do you want to officially approve?

Thanks, all!

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pllim commented Mar 6, 2026

Also, precommit got stuck, so please rebase?

@astrofrog astrofrog force-pushed the support-uncompressed-data branch from 162d385 to e5a3571 Compare March 6, 2026 22:16
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astrofrog commented Mar 6, 2026

@saimn should definitely review this before it is merged

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astrofrog commented Mar 16, 2026

@saimn - just to check, as you said LGTM higher up, can you approve this if you are happy with it?

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saimn approved these changes Mar 16, 2026
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Thanks @astrofrog !

@saimn saimn merged commit ab1ba09 into astropy:main Mar 16, 2026
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meeseeksmachine pushed a commit to meeseeksmachine/astropy that referenced this pull request Mar 16, 2026
@saimn @meeseeksmachine
Backport PR astropy#19363: Add support for reading compressed FITS fi…
dcac212 
…les with UNCOMPRESSED_DATA
@meeseeksmachine meeseeksmachine mentioned this pull request Mar 16, 2026
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pllim added a commit that referenced this pull request Mar 16, 2026
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Merge pull request #19441 from meeseeksmachine/auto-backport-of-pr-19…
04b4da2 
…363-on-v7.2.x

Backport PR #19363 on branch v7.2.x (Add support for reading compressed FITS files with UNCOMPRESSED_DATA)
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backport-v7.2.x on-merge: backport to v7.2.x Bug io.fits Ready-for-final-review

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Successfully merging this pull request may close these issues.

FITS Compressed File Opening Issue Version 5.3 fails to correctly read (some) rice-compressed files.

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