Similar error as #2437 but from macos client using GUI, when .ssh/config entry has a 'Port 22' (i.e. I believe any explicit numeric Port line, default or not, but it is the default value of 22 in my case).
Of course the GUI-form forces a value to be entered for the Port field, and I enter 22 there in any case (this is probably not relevant).
I used the download: Xpra-Python2-x86_64-3.0.1-r24240.dmg For my case, all these are different: OS, python2 not 3, version 3.0.1 not 3.0, GUI (not cmd-line 'xpra attach'), '%d' not '%i'.
% Xpra_Version_info Build: * local_modifications : 0 * revision : 24240 * version : 3.0.1 Platform: * architecture : 64bit, * machine : x86_64 * name : Mac OS X 10.13.6 * platform : Darwin-17.7.0-x86_64-i386-64bit * processor : Intel(R) Core(TM)2 Duo CPU P8600 @ 2.40GHz * release : 17.7.0 * sys : darwin * sysrelease : 10.13.6 Host: * byteorder : little * gid : 20 * hostname : blah.local * pid : 55927 * pyobjc.version : 5.2 * python - bits : 64 - full_version : 2.7.16 (default, Sep 30 2019, 11:55:05) \n[GCC 4.2.1 Compatible Apple LLVM 7.3.0 (clang-703.0.31)] - version : 2.7.16 * uid : 501
Launcher error in screenshot
Thanks for the bug report, this is fixed in r24363 and will be in the next stable update. In the meantime, you could apply this by hand as the change is quite small.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2473