Creating a virtualenv started to fail with Python version 2.7.11 some time between Sep 6 and 26. Corresponding commits from the github repository ouspg/urlhandlers only had changes in documentation, not in code. Relevant builds in https://circleci.com/gh/ouspg/urlhandlers are 204 (still working) and 206 (deleted LICENSE, build failing).
The error is related to installing the wheel package with pip when creating the virtualenv:
/opt/circleci/python/2.7.11/bin/python2.7 /opt/circleci/.pyenv/versions/2.7.11/bin/virtualenv /home/ubuntu/virtualenvs/venv-system
...
/home/ubuntu/virtualenvs/venv-system/bin/python2.7 -c 'import sys, pip; sys.exit(pip.main(["install", "--ignore-installed"] + sys.argv[1:]))' setuptools pip wheel
...
File "/opt/circleci/python/2.7.11/lib/python2.7/site-packages/virtualenv_support/pip-8.0.2-py2.py3-none-any.whl/pip/_vendor/requests/adapters.py", line 447, in send
raise SSLError(e, request=request)
SSLError: [Errno 20] Not a directory
The build links contain the full error messages. Debugging the build with a ssh connection and omitting the wheel package (–no-wheel) resulted in a successful virtualenv creation. I made a branch with a newer Python version in circle.yml, and it built successfully (build 216),