Upgrade python in a virtualenv

If you happen to be using the venv module that comes with Python 3.3+, it supports an --upgrade option. Per the docs:

Upgrade the environment directory to use this version of Python, assuming Python has been upgraded in-place

python3 -m venv --upgrade ENV_DIR

Did you see this? If I haven't misunderstand that answer, you may try to create a new virtualenv on top of the old one. You just need to know which python is going to use your virtualenv (you will need to see your virtualenv version).

If your virtualenv is installed with the same python version of the old one and upgrading your virtualenv package is not an option, you may want to read this in order to install a virtualenv with the python version you want.

EDIT

I've tested this approach (the one that create a new virtualenv on top of the old one) and it worked fine for me. I think you may have some problems if you change from python 2.6 to 2.7 or 2.7 to 3.x but if you just upgrade inside the same version (staying at 2.7 as you want) you shouldn't have any problem, as all the packages are held in the same folders for both python versions (2.7.x and 2.7.y packages are inside your_env/lib/python2.7/).

If you change your virtualenv python version, you will need to install all your packages again for that version (or just link the packages you need into the new version packages folder, i.e: your_env/lib/python_newversion/site-packages)

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 .Pythonrm bin/pip{,2,2.7}rm bin/python{,2,2.7}rm -r include/python2.7rm lib/python2.7/*rm -r lib/python2.7/distutilsrm lib/python2.7/site-packages/easy_install.*rm -r lib/python2.7/site-packages/piprm -r lib/python2.7/site-packages/pip-*.dist-inform -r lib/python2.7/site-packages/setuptoolsrm -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