[python] Upgrade python in a virtualenv

Updated again: The following method might not work in newer versions of virtualenv. Before you try to make modifications to the old virtualenv, you should save the dependencies in a requirement file (pip freeze > requirements.txt) and make a backup of it somewhere else. If anything goes wrong, you can still create a new virtualenv and install the old dependencies in it (pip install -r requirements.txt).

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):

cd <EXISTING_ENV_PATH>
rm .Python
rm bin/pip{,2,2.7}
rm bin/python{,2,2.7}
rm -r include/python2.7
rm lib/python2.7/*
rm -r lib/python2.7/distutils
rm lib/python2.7/site-packages/easy_install.*
rm -r lib/python2.7/site-packages/pip
rm -r lib/python2.7/site-packages/pip-*.dist-info
rm -r lib/python2.7/site-packages/setuptools
rm -r lib/python2.7/site-packages/setuptools-*.dist-info

Finally, re-create your virtual environment:

virtualenv <EXISTING_ENV_PATH>

By doing so, old Python core files and standard libraries (plus setuptools and pip) are removed, while the custom libraries installed in site-packages are preserved and working, as soon as they are in pure Python. Binary libraries may or may not need to be reinstalled to function properly.

This worked for me on 5 virtual environments with Django installed.

BTW, if ./manage.py compilemessages is not working afterwards, try this:

brew install gettext && brew link gettext --force

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