Deal with several package versions in python virtualenv

Question

I'm using a computation server where I have no root privileges, so in order to be able to install whatever libraries I want, I created a virtualenv with --system-site-packages for python 2.6.

Then, inside the virtual environment, I installed numpy version 1.8.2 because the system numpy version (1.3.0) is too old for my requirements:

numpy - 1.3.0 - active development (/usr/lib64/python2.6/site-packages)

numpy - 1.8.2 - non-active

I need the --system-site-packages option because I'm using some system libraries that I cannot install in the virtual environment. However I am not able to tell the virtual environment to use the most recent version of numpy.

Does anyone know how to select version 1.8.2 in the virtual environment? I tried with pkg_resources.require('numpy==1.8.2') but I got the error:

pkg_resources.VersionConflict: (numpy 1.3.0 (/usr/lib64/python2.6/site-packages), Requirement.parse('numpy==1.8.2'))

Is there some way of telling the virtual environment to look for libraries in the virtual virt2/lib64/python2.6/site-packages folder before looking in the system's /usr/lib64/python2.6/site-packages folder?

Answer 1

It is likely that ou have been bitten by issue #461 and currently(as of August-2014) you CANNOT upgrade any system-inherited package because virtualenv 's paths are ordered AFTER any system-paths within sys.path .

Your workaround it to move the (usually) last sys-path entry one position above:

• Re-ordering sys.path with python-code., For instance, assuming that the index of your virtualenv's site-packages is the last one, you have to make sure that the following code runs before any other code:

   import sys; sys.path.insert(0, sys.path.pop(-1)) 

• modify similarly your PYTHONPATH environment-variable before executing python-interpreter (see question #10738919 and ).