cat >req.txt <<EOF
setuptools>=18.5
html5lib
EOF

virtualenv testenv
testenv/bin/pip install -r req.txt

Collecting setuptools>=18.5 (from -r req.txt (line 1))
  Using cached setuptools-24.0.3-py2.py3-none-any.whl
Collecting html5lib (from -r req.txt (line 2))
  Using cached html5lib-0.999999999.tar.gz
    Complete output from command python setup.py egg_info:
    html5lib requires setuptools version 18.5 or above; please upgrade before installing (you have 18.2)

    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /private/var/folders/49/p3xmv77x6fnb2lwl5kpvmvs40000gp/T/pip-build-0vYISn/html5lib
You are using pip version 7.1.2, however version 8.1.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.