Comment 2 for bug 1429521

Thanks for taking your time to report this issue and help making Ubuntu better.

I was not able to reproduce this issue when I tested on an up-to-date Vivid system:
$ python3 -m flake8 -vv foo.py
checking foo.py
pass

Looks like the underlying problem occurs when it calls pep8, which version of pep8 do you have installed?

$ apt-cache policy python3-flake8
python3-flake8:
  Installed: 2.2.2-1ubuntu1
  Candidate: 2.2.2-1ubuntu1
  Version table:
 *** 2.2.2-1ubuntu1 0
        500 http://no.archive.ubuntu.com/ubuntu/ vivid/main amd64 Packages
        100 /var/lib/dpkg/status

$ apt-cache policy python3-pep8
python3-pep8:
  Installed: 1.5.7-2
  Candidate: 1.5.7-2
  Version table:
 *** 1.5.7-2 0
        500 http://no.archive.ubuntu.com/ubuntu/ vivid/main amd64 Packages
        100 /var/lib/dpkg/status