According to the pyflakes' NEWS.rst, the default output format changed
recently:
2.2.0 (2020-04-08) - Include column information in error messages
So the lines now read:
contrib/perf.py:149:15 undefined name 'xrange' mercurial/hgweb/server.py:427:13 undefined name 'reload' mercurial/util.py:2862:24 undefined name 'file'
This is a graft of a similar fix that ended up on default.