python-dev installation error: ImportError: No mod

Question

I am Debian user, and I want to install python-dev, but when I run the code in the shell as a root:

# aptitude install python-dev

I get the following error:

Traceback (most recent call last):       
  File "/usr/bin/apt-listchanges", line 28, in <module>
    import apt_pkg
ImportError: No module named apt_pkg

What seems to be the problem and how can I resolve it?

Answer 1

This error will often occur when a newer version of python has been installed alongside an older version e.g;

• Ubuntu 18.04.1 ships with python version 3.6.6
• Installed ppa:deadsnakes/python3.7.1 or alternative

• Run a command that uses the apt_pkg module and get an error such as;

      from CommandNotFound.db.db import SqliteDatabase
  File "/usr/lib/python3/dist-packages/CommandNotFound/db/db.py", line 5, in <module>
      import apt_pkg
  

When we install a non-distro python3 version with apt it will set a shared module directory to be that of python3 most usually it will /usr/lib/python3.

Most of the time this will be ok, but under some circumstances the different versions of python rely on different libraries or shared objects/libraries then the other python version does so as other answers have pointed out we need to link the .SO to the correct python version. So if we have python3.6 installed on a 64bit system then the apt_pkg .SO link would be

sudo ln -s apt_pkg.cpython-36m-x86_64-linux-gnu.so pt_pkg.so

But the problem lies in the fact that when we install a newer python version the link will update to point to the newest python version, which leads to the error of apt_pkg module not being found. By checking which version of python ships with your distro you can create the link as shown above. Or we use a method to offer the command a choice of python versions to link the .SO such as;

sudo ln -s apt_pkg.cpython-{36m,35m,34m}-x86_64-linux-gnu.so pt_pkg.so

Because python will create this link to the newest installed python version we give the command the option to choose from 3 python versions, of which it will choose the highest version given.

Answer 2

Make sure you have a working python-apt package. You could try and remove and install that package again to fix the problem with apt_pkg.so not being located.

apt-get install python-apt

Answer 3

I met this problem when doing sudo apt-get update. My env is debian8, with python2.7 + 3.4(default) + 3.5.

The following code will only re-create a apt_pkg....so file for python 3.5

sudo apt-get install python3-apt --reinstall

The following code solved my problem,

cd /usr/lib/python3/dist-packages
sudo ln -s apt_pkg.cpython-{35m,34m}-x86_64-linux-gnu.so

So, obviously, python3-apt checks the highest python version, instead of the current python version in use.

Answer 4

For some reason my install was missing apt_pkg.so in the python3 dist-packages dir. (apt_pkg.cpython-33m-x86_64-linux-gnu.so was there?!) but and I had to make a symlink apt_pkg.so -> apt_pkg.cpython-33m-x86_64-linux-gnu.so in /usr/lib/python3/dist-packages

I'm not sure whether my upgrade was broken or why this was the case. It occured after trying to upgrade (precise->raring->quantal upgrade)

Answer 5

Solve it by this:

/usr/lib/python3/dist-packages# cp apt_pkg.cpython-34m-i386-linux-gnu.so apt_pkg.so

Or:

/usr/lib/python3/dist-packages# cp apt_pkg.cpython-35m-x86_64-linux-gnu.so apt_pkg.so

Basically, if you get a No such file or directory just ls to try to get the right name.

Answer 6

Just in case it helps another, I finally solved this problem, that was apparently caused by python version conflicts, by redirecting the link python3, then redirecting it to the right python version:

sudo rm /usr/bin/python3
sudo ln -s /usr/bin/python3.4

You may need to enter the correct python version, found with:

python3 -V