How to ignore python module in ~/.local/lib/python2.7/site-packages?

Question

I have a python package dateutil in the ~/.local/lib/python2.7/site-packages directory as well as one in /usr/lib/python2.7/dist-packages/dateutil. When I try to run an executable from kalibr (a camera calibration tool, I downloaded the CDE), rrule.py from the dateutil package in ~/.local/lib/python2.7/site-packages throws an error "ImportError: No module named fractions". I can get kalibr running, by removing said dateutil package (s.t. it uses the one in /usr/lib/python2.7/dist-packages/dateutil) but I fear that this will have some implications on other projects.

So I figured that the basic problem here is that python prefers the dateutil package in ~/.local/lib/python2.7/site-packages over the one in /usr/lib/python2.7/dist-packages/dateutil.

How can I make python prefer the latter one?

(I am using Ubuntu 16.04)

Answer 1

I don't think there's a way to choose which directory to load packages from on a per-package basis, but you can change the order in which Python looks for packages. The order is reflected in sys.path. The default package search path is influenced by site-specific files, but mostly it's:

1. The current directory.
2. Directories listed in the PYTHONPATH environment variable.
3. The standard library that comes with Python itself.
4. The dist-packages directory under ~/.local (the user site-packages directory), which is where pip install --user installs things. You can change the path to this directory by setting the environment variable PYTHONUSERBASE and disable it completely by setting PYTHONNOUSERSITE to a non-empty value.
5. The dist-packages directory under /usr/local, which is where pip install installs things.

So if a directory needs to be traversed first, you can put it in PYTHONPATH. In your case, there's a good chance that you can just disable ~/.local to run kalibr.

env PYTHONNOUSERSITE=1 kalibr

To see the package search path, run

python -m site

(All of this applies to Python3 as well.)

(Generally, preferring packages under ~/.local to packages under /usr is the right thing. Ideally, packages would always be backward compatible, and if you ran into an incompatibility, you'd just install the latest version under ~/.local with pip install --user. But in the real world, this doesn't always work out.)