Updated: I changed the answer 5 months after I originally answered. The following method is more convenient and robust.
Side effect: it also fixes the Symbol not found: _SSLv2_method exception when you do import ssl in a virtual environment after upgrading Python to v2.7.8.
Notice: Currently, this is for Python 2.7.x only.
If you're using Homebrew Python on OS X, first deactivate all virtualenv, then upgrade Python:
brew update && brew upgrade python Run the following commands (<EXISTING_ENV_PATH> is path of your virtual environment):