This may be caught in a transition from python2.7 to python3 in Debian. python2.7 is approaching end of life and will be deprecated soon. I see that libxml2 is support with another library for python3;

python3-lxml - pythonic binding for the libxml2 and libxslt libraries

It may be that the chirp application has not yet updated their python dependencies.

Thanks. I understand there is a transition here. I will close this, but

1. I thought Amber was essentially Buster with PureOS modifications? Why would the 'old' package be in Buster and not Amber?
2. Why is this package listed as part of Amber, but it is not actually there?

Amber is Buster, yes.

I definitely see it in Amber;

Our software search tool;

https://software.pureos.net/package/bin/amber/python-libxml2

$ apt-cache search python-libxml2
python-libxml2 - Python bindings for the GNOME XML library
python-libxml2-dbg - Python bindings for the GNOME XML library (debug extension)

I don't understand why it is not showing up for you. What do you see when you do;
apt-cache search python-libxml2

This is what I see for that command:

python-libxml2 - Python bindings for the GNOME XML library
python-libxml2-dbg - Python bindings for the GNOME XML library (debug extension)

I also see that package in the link you provided, which is different from the repository. But, as I said in my initial information, I see it fine with 'apt', but I do not see the package in 'repo.puri.sm'.

Err:1 https://repo.puri.sm/pureos amber/main amd64 python-libxml2 amd64 2.9.4+dfsg1-7+b3
  404  Not Found [IP: 138.201.228.45 443]

(Is the IP resolving correctly?)

But the issue is not that you can't see it in the repos - just that it won't install on your machine, right?

No. The package does not appear to be in the actual repos (repo.puri.sm), even though 'apt' and your link say it should be there.

You can try the link as reported by 'apt' yourself.

I think if the package were actually in the repository, I could install it without any issues.

What does sudo apt-update && sudo apt install python-libxml2 say?

I don't think it is an IP issue because the IP resolves correctly. I think it is a version issue.

As I mentioned in my initial post, I already tried the 'update' and the --fix-missing, so your commands yield the same errors as I have mentioned before. Have you checked that the file is actually on repo.puri.sm?

sudo apt update && sudo apt install python-libxml2 
Hit:1 http://ppa.launchpad.net/opencpn/opencpn/ubuntu bionic InRelease
Hit:2 https://repo.puri.sm/pureos amber InRelease                              
Hit:3 https://repo.pureos.net/pureos amber-security InRelease                  
Hit:4 https://repo.pureos.net/pureos amber-updates InRelease
Reading package lists... Done
Building dependency tree       
Reading state information... Done
All packages are up to date.
Reading package lists... Done
Building dependency tree       
Reading state information... Done

<snipped some autoremove messages that just appeared>

The following NEW packages will be installed:
  python-libxml2
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 206 kB of archives.
After this operation, 982 kB of additional disk space will be used.
Err:1 https://repo.puri.sm/pureos amber/main amd64 python-libxml2 amd64 2.9.4+dfsg1-7+b3
  404  Not Found [IP: 138.201.228.45 443]
E: Failed to fetch https://repo.puri.sm/pureos/pool/main/libx/libxml2/python-libxml2_2.9.4+dfsg1-7+b3_amd64.deb  404  Not Found [IP: 138.201.228.45 443]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

Jeremiah, you were correct. There is a difference in versions, but I do not know why my apt database has a different one, i.e. python-libxml2_2.9.4+dfsg1-7+b3_amd64.deb. I tried to purge it and get the new listing, but to no avail.

I guess I had a brain freeze; I could have looked on the repository myself with https. (I guess I am used to getting errors when I try to access directories only.) When I did, I saw the file: python-libxml2_2.9.4-dfsg1-7-deb10u1_amd64.deb.

This is consistent with the link you posted earlier.

I'll play around with this and see if I can somehow get it to see the new one. Thanks for your help and ideas.

Glad you tracked down the issue! Nice sleuthing!

BTW, though I do not know what caused this, I am glad it happened. I had 86 updates awaiting that I never knew about.