Python 3 cannot import third party packages

Question

I have Python version 3.5.2 and I have pip3, so I did

sudo pip3 install pyqt5

That got installed in /usr/local/lib/python3.5/dist-packages

However when I enter my python 3 interpreter and type

import PyQt5

it gives me an error that it can't find the module named PyQt5.

So I tried adding the /usr/local/lib/python3.5/dist-packages path to PYTHONPATH by doing

export PYTHONPATH=$PYTHONPATH:/usr/local/lib/python3.5/dist-packages

but that didn't fix anything. How do I make Python 3.5.2 detect PyQt5?

@George ah sorry, I forgot to mention that I did try sudo from the very start. I edited my question to portray that. All it says is "pyqt5 in /usr/local/lib/python3.5/dist-packages" — Shadowfax, Dec 06 '16 at 18:46
try running sudo -H pip3 install pyqt5 this time lets see what happens. Quite strange as I have successfully installed it on my system, also do sudo apt update && sudo apt dist-upgrade before the pips command — George Udosen, Dec 06 '16 at 19:12
Oh, I just noticed after doing python 3 import site; site.getsitepackages() that it only finds /usr/local/lib/python3.5/site-packages, and it doesn't list the /usr/local/lib/python3.5/dist-packages that the actual modules are installed in. Do you think that might be my problem? — Shadowfax, Dec 06 '16 at 19:15
@George hmm well I tried what you asked, but it still says Requirement already satisfied: pyqt5 in /usr/local/lib/python3.5/dist-packages Requirement already satisfied: sip in /usr/local/lib/python3.5/dist-packages (from pyqt5) Maybe it's a site packages issue... — Shadowfax, Dec 06 '16 at 19:24
about the importation of dist package I should think so. — George Udosen, Dec 06 '16 at 19:30
okay, so inside the python 3 interpreter I did import sys; sys.path.insert(0, "/usr/local/lib/python3.5/dist-packages") and it was able to import PyQt5 after that. Do you know how to make python3 always do this without me needing to code it into every script? — Shadowfax, Dec 06 '16 at 19:30
I am not an expert on that but i think only native python libs can be used this way... but a template might make it easier — George Udosen, Dec 06 '16 at 19:43

score 5 · Answer 1 · edited May 23 '17 at 12:39

Thanks to George I slowly got to the answer. The root of the problem lies in that I installed my Python 3.5.2 version from a source rather than from the Ubuntu aptitude package manager.

Basically, if Python is installed from a source, then, to look for 3rd party packages, it uses /usr/local/lib/python3.5/site-packages, but if it was installed using apt, then Python looks in /usr/local/lib/python3.5/dist-packages. This is to make sure that the several Python versions don't get tangled up. Here is another question that explains: what is the difference between dist-packages and site-packages?.

Solution:

My Python3 installation was looking into site-packages and ignoring dist-packages, so I added a path file to make it look inside dist-packages as well.

cd /usr/local/lib/python3.5/site-packages
sudo vim dist-packages.pth
(Press i to go into insert mode inside Vim)
../dist-packages
:x (and Press Enter/Return)

Now when Python looks inside /site-packages, it finds dist-packages.pth which makes it go into /dist-packages.

Other Solution:

Someone else had a problem exactly the reverse of mine, where their Python installation only looked inside /dist-packages, so they used the exact same method as above except instead of making a dist-packages.pth file (containing ../dist-packages) inside /site-packages, they made a site-packages.pth file (containing ../site-packages inside /dist-packages.

Check if it worked:

The easy way to check if this worked is to go into your Python interpreter and print sys.path. It should now contain both package paths:

charliebrown@playground:/usr/local/lib/python3.5/site-packages$ python3
Python 3.5.2 (default, Nov 19 2016, 02:36:25) 
[GCC 5.4.0 20160609] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys; print(sys.path)
['', '/usr/local/lib/python35.zip', '/usr/local/lib/python3.5',     '/usr/local/lib/python3.5/plat-linux', '/usr/local/lib/python3.5/lib-dynload', 
'/usr/local/lib/python3.5/site-packages', '/usr/local/lib/python3.5/dist-packages']

I hope this helps someone one day...

Python 3 cannot import third party packages

1 Answers1