I was seeing this same error, but in a different way, and managed to fix it up. Basically default python27 in the mac seems broken.
On my mac, I saw this because I used port to install python27 but not virtualenv, installing the port version of virtualenv brought the fix into my virtualenv when running ./run-tests.sh
Interestingly tox correctly picked up the port install of python27, so never showed this issue.
I was seeing this same error, but in a different way, and managed to fix it up. Basically default python27 in the mac seems broken.
On my mac, I saw this because I used port to install python27 but not virtualenv, installing the port version of virtualenv brought the fix into my virtualenv when running ./run-tests.sh
Interestingly tox correctly picked up the port install of python27, so never showed this issue.