That is some nice progress!

I built and installed the python37-Qt4 bindings. (Aside: it turned out that they conflict with the python27-Qt4 bindings, because it installs some files with the same name for both. I fixed that up in pkgsrc for Qt5. Fortunately, here the only user of python27-Qt4 was qbzr, so I won't bother doing the same work for py-Qt4 just yet).

I also updated the packaging of breezy to 3.1.0. I was a bit let astray by much higher version numbers already in the release notes, so I had to try out which version actually exists.

Then I tried "brz qlog" (which tends to be the GUI thing I use most, for basically all version control systems) in a directory where actually a repository exists. Indeed I got the window I'm used to.

There are of course some loose ends. I noticed that various subcommands need "patiencediff" which I do seem to have for python 2.7 in bzrlib. So I guess that needs to be added to breezy.

Also I tried "brz qlog" outside a repository, which gave me a spectactular stacktrace. I'm sure those are all small points that are already on a list somewhere :-)

(interestingly enough, in some directories I get the stack trace. In others I get a nice error message "brz: ERROR: Not a branch: "/mnt/vol1/rhialto/cvs/other/qbrz/"." So I thought I'd add the stack trace for reference:

murthe.10:.../pkgsrc/devel/breezy$ brz qlog
brz: ERROR: TypeError: __str__ returned non-string (type CVSDirFormat)

Traceback (most recent call last): 
  File "/usr/pkg/lib/python3.7/site-packages/breezy/plugins/qbrz/lib/trace.py", 
line 378, in reports_exception_decorate
    return f(*args, **kargs)
  File "/usr/pkg/lib/python3.7/site-packages/breezy/plugins/qbrz/lib/log.py", line 244, in load
    branches, primary_bi, file_ids = self.get_branches_and_file_ids()
  File "/usr/pkg/lib/python3.7/site-packages/breezy/plugins/qbrz/lib/log.py", line 285, in get_branches_and_file_ids
    tree, br, repo, fp = ControlDir.open_containing_tree_branch_or_repository(location)
  File "/usr/pkg/lib/python3.7/site-packages/breezy/controldir.py", line 852, in open_containing_tree_branch_or_repository
    controldir, relpath = klass.open_containing(location)
  File "/usr/pkg/lib/python3.7/site-packages/breezy/controldir.py", line 773, in open_containing
    return klass.open_containing_from_transport(transport)
  File "/usr/pkg/lib/python3.7/site-packages/breezy/controldir.py", line 794, in open_containing_from_transport
    result = klass.open_from_transport(a_transport)
  File "/usr/pkg/lib/python3.7/site-packages/breezy/controldir.py", line 761, in open_from_transport
    format.check_support_status(_unsupported)
  File "/usr/pkg/lib/python3.7/site-packages/breezy/plugins/cvs/__init__.py", line 60, in check_support_status
    raise CVSUnsupportedError(self)
breezy.plugins.cvs.CVSUnsupportedError: <unprintable CVSUnsupportedError object>

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/pkg/lib/python3.7/site-packages/breezy/plugins/qbrz/lib/util.py", line 956, in run_in_loading_queue
    f(*args, **kargs)
  File "/usr/pkg/lib/python3.7/site-packages/breezy/plugins/qbrz/lib/uifactory.py", line 32, in decorate
    r = f(*args, **kargs)
  File "/usr/pkg/lib/python3.7/site-packages/breezy/plugins/qbrz/lib/trace.py", line 382, in reports_exception_decorate
    report_exception(type=type, window=args[0].window())
  File "/usr/pkg/lib/python3.7/site-packages/breezy/plugins/qbrz/lib/trace.py", line 125, in report_exception
    error_type = _breezy_report_exception(exc_info, err_file)
  File "/usr/pkg/lib/python3.7/site-packages/breezy/trace.py", line 525, in report_exception
    report_user_error(exc_info, err_file)
  File "/usr/pkg/lib/python3.7/site-packages/breezy/trace.py", line 558, in report_user_error
    err_file.write(("brz: ERROR: %s\n" % (str(exc_info[1]),)))
TypeError: __str__ returned non-string (type CVSDirFormat)

brz 3.1.0 on python 3.7.7 (NetBSD-9.0-amd64-x86_64-64bit-ELF)
arguments: ['/usr/pkg/bin/brz', 'qlog']
plugins: bash_completion[3.1.0], changelog_merge[3.1.0],
    commitfromnews[3.1.0], cvs[3.1.0], darcs[3.1.0], email[3.1.0],
    fastimport[3.1.0], flake8[unknown], fossil[3.1.0], github[3.1.0],
    gitlab[3.1.0], hg[3.1.0], launchpad[3.1.0], mtn[3.1.0],
    netrc_credential_store[3.1.0], news_merge[3.1.0], po_merge[3.1.0],
    propose[3.1.0], qbrz[0.3.1dev], quilt[unknown], repodebug[3.1.0],
    rewrite[unknown], stats[3.1.0], svn[3.1.0], upload[3.1.0],
    weave_fmt[3.1.0], zsh_completion[3.1.0]
encoding: 'iso8859-1', fsenc: 'iso8859-1', lang: None

*** Bazaar has encountered an internal error.  This probably indicates a
    bug in Bazaar.  You can help us fix it by filing a bug report at
        https://bugs.launchpad.net/brz/+filebug
    including this traceback and a description of the problem.


There seems to be a suggestion that this only happens in CVS directories, which I can imagine are not so common these days.

Good job!