Printing not working. No module named 'cups'

[Gokev79]

Describe the bug
Printing with HTML5 client not working.

To Reproduce
Steps to reproduce the behavior:

1. /usr/bin/xpra start :100 --bind-tcp=localhost:10000 --start-child="firefox" --exit-with-children -d printing
2. Connect with HTML5 client

System Information (please complete the following information):

• Server OS: OL 9
• Client OS: HTML5-Client
• Xpra Server Version: xpra v6.1.2-r1
• Xpra Client Version HTML5-Client = Version 16.1

Additional context
Error:
printing module is not installed: No module named 'cups'
init_printing() printing=False

But CUPS is installed: python3-cups.x86_64 2.0.1-10.el9 @ol9_appstream-x86_64

Total output xpra session log:

# cat /run/xpra/100/server.log
2024-09-25 16:16:57,582 Error: cannot enable SSH socket upgrades
2024-09-25 16:16:57,583  `paramiko` module not found
2024-09-25 16:16:57,583 created tcp socket 'localhost:10000'
Socket path '/tmp/.X11-unix/X100' not found
2024-09-25 16:16:57,596 no uinput module (not usually needed)

X.Org X Server 1.20.11
X Protocol Version 11, Revision 0
Build Operating System:  5.15.0-200.131.27.1.el9uek.x86_64
Current Operating System: Linux ts-wdl-01 5.15.0-210.163.7.el9uek.x86_64 #2 SMP Tue Sep 10 17:46:37 PDT 2024 x86_64
Kernel command line: BOOT_IMAGE=(hd0,gpt2)/vmlinuz-5.15.0-210.163.7.el9uek.x86_64 root=/dev/mapper/ocivolume-root ro LANG=en_US.UTF-8 console=tty0 console=ttyS0,115200 rd.luks=0 rd.md=0 rd.dm=0 rd.lvm.vg=ocivolume rd.lvm.lv=ocivolume/root rd.net.timeout.dhcp=10 rd.net.timeout.carrier=5 netroot=iscsi:169.254.0.2:::1:iqn.2015-02.oracle.boot:uefi rd.iscsi.param=node.session.timeo.replacement_timeout=6000 net.ifnames=1 nvme_core.shutdown_timeout=10 ipmi_si.tryacpi=0 ipmi_si.trydmi=0 libiscsi.debug_libiscsi_eh=1 loglevel=4 crash_kexec_post_notifiers crashkernel=1G-64G:448M,64G-:512M
Build Date: 18 January 2024  12:00:00AM
Build ID: xorg-x11-server 1.20.11-24.el9
Current version of pixman: 0.40.0
        Before reporting problems, check http://wiki.x.org
        to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
        (++) from command line, (!!) notice, (II) informational,
        (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(++) Log file: "/run/xpra/100/Xorg.log", Time: Wed Sep 25 16:16:57 2024
(++) Using config file: "/etc/xpra/xorg.conf"
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
2024-09-25 16:16:58,804 debug enabled for ['xpra.net.file_transfer', 'printing']
2024-09-25 16:16:58,805 debug enabled for ['xpra.server.mixins.fileprint', 'printing']
2024-09-25 16:16:58,833 pointer device emulation using XTest
2024-09-25 16:16:58,849 serving html content from '/usr/share/xpra/www'
2024-09-25 16:16:58,850 wrote pid 34065 to '/run/xpra/100/server.pid'
2024-09-25 16:16:58,870 created unix domain sockets:
2024-09-25 16:16:58,870  '/run/user/0/xpra/ts-wdl-01-100'
2024-09-25 16:16:58,870  '/run/xpra/ts-wdl-01-100'
2024-09-25 16:16:58,870  '/root/.xpra/ts-wdl-01-100'
2024-09-25 16:16:58,870  '/run/xpra/100/socket'
2024-09-25 16:16:58,870 created abstract sockets:
2024-09-25 16:16:58,870  '@xpra/100'
2024-09-25 16:16:58,870 local unix domain sockets we can use for printing: ['/run/user/0/xpra/ts-wdl-01-100', '/run/xpra/ts-wdl-01-100', '/root/.xpra/ts-wdl-01-100', '/run/xpra/100/socket', '@xpra/100']
2024-09-25 16:16:58,870 xvfb pid 34130
2024-09-25 16:16:58,878 setting dummy crtc and output 0 to:
2024-09-25 16:16:58,878  1024x768 50Hz (271x203 mm, dpi=96)
2024-09-25 16:16:58,879 monitor 0 is 'VFB-0' 1024x768
2024-09-25 16:16:58,887 D-Bus notification forwarding is available
2024-09-25 16:16:58,897 Warning: cannot watch for application menu changes without pyinotify:
2024-09-25 16:16:58,897  No module named 'pyinotify'
2024-09-25 16:16:58,898 printing module is not installed: No module named 'cups'
2024-09-25 16:16:58,898 init_printing() printing=False
2024-09-25 16:16:58,960 15.2GB of system memory
2024-09-25 16:16:59,091 xpra is ready.
2024-09-25 16:16:59,092 xpra X11 seamless server version 6.1.2-r1
2024-09-25 16:16:59,092  uid=0 (root), gid=0 (root)
2024-09-25 16:16:59,092  running with pid 34065 on Linux OracleLinux 9.4
2024-09-25 16:16:59,092  cpython 3.11
2024-09-25 16:16:59,095  connected to X11 display :100 with 24 bit colors
2024-09-25 16:16:59,161 loaded 16 start menu entries from 2 sub-menus in 0.2 seconds
2024-09-25 16:16:59,421 OpenGL is supported on display ':100'
2024-09-25 16:16:59,421  using 'llvmpipe (LLVM 17.0.6, 256 bits)' renderer
2024-09-25 16:16:59,422 started command `firefox` with pid 34181
2024-09-25 16:16:59,423 started command `ibus-daemon` with pid 34182
2024-09-25 16:16:59,424 wrote pid 34182 to '/run/xpra/100/ibus-daemon.pid'

[totaam]

But CUPS is installed: python3-cups.x86_64 2.0.1-10.el9 @ol9_appstream-x86_64

This is python3-cups for el9 (which is python3.9 IIRC), but your xpra server is running:

2024-09-25 16:16:59,092 cpython 3.11

You would need to install python3.11-cups for xpra to be able to load it.

This is not provided by your distro or the xpra repo.
You could install it globally via pip.
Another option would be to downgrade xpra to the 5.x LTS branch which still supports python3.9.